Department: Chemical Physics ![[clear]](close-x.png "Remove this limiter")
32 matches in the database.
These are records: 1 - 30.
[1] [2]
1.
Chang, Qiang.
Continuous-time random-walk simulation of surface kinetics.
Degree: PhD, Chemical Physics, 2007, Ohio State University
► A simulation technique, continuous-time random-walk(CTRW) Monte Carlo simulation, is introduced to model…
(more)
▼ A simulation technique, continuous-time random-walk(CTRW) Monte Carlo simulation, is introduced to model surface kinetics on interstellar grains. The new technique is able to solve problems studied previously with rate equation and master equation approaches. Inhomogeneous and rough surface models are also introduced, and the CTRW Monte Carlo method is found to be very suitable for kinetics simulations on these surfaces. We first try to solve the famous molecular hydrogen formation problem with an inhomogeneous surface model and with this simulation technique. We introduce the concept of effective rate coefficients to couple this technique into full gas-grain network simulations. The dependence of effective rate coefficients on temperature and H flux is studied. We also introduce a new mathematical model to use the CTRW for full gas-grain network simulation in dense clouds. The surface network is a well studied H, O and CO system. We find that rough surface models can help to explain observation.
Advisors/Committee Members: Herbst, Eric.
More Like This
2.
Chen, Chia-Yi.
Chemically Tailored Organic-Based Magnets to Exploit Optical Control of Magnetization and Depth-Resolved Magnetization in V[TCNE]x~2 via Polarized Neutron Reflectivity.
Degree: PhD, Chemical Physics, 2010, Ohio State University
► Organic-based magnets have attracted much attention in recent decades as numerous benefits…
(more)
▼ Organic-based magnets have attracted much attention in recent decades as numerous benefits of this class of materials have been touted. In particular, chemical tailorability and potential use in practical applications paint a promising picture for the future of organic-based magnets in the field of spintronics. In the first part of this work, chemically tailoring organic-based magnets with optical-controllable functionality is realized through modifying organic molecules with azo functional groups. Two new optical-switchable electron acceptors, 3,3’-di-(1,1,2-tricyanovinyl)azobenzene (DTCVAzo) and 3,-(1,1,2-tricyanovinyl)azobenzene (TCVAzo), were synthesized and characterized. Their associated organic-based magnets prepared from reaction with V(CO)6 exhibit magnetic ordering below 60 and 126 K, respectively. At low temperatures the magnetization of both magnets decreases upon illumination with UV light whereas no change in magnetization is observed with subsequent visible light irradiation. The reduced magnetization is a long-lived metastable state in the dark and at low temperatures (> 106 s at 15 K) but can be fully recovered by thermal treatment above 240 K. A further study was extended to a solid solution magnet prepared from the reaction of V(CO)6 and a mixture of tetracyanoethylene (TCNE) and TCVAzo. An interesting multi-step photomagnetic response is observed in the solid solution at low temperatures with the illumination of UV or visible light. The correlation between the photoinduced magnetization of the organic-based magnets and the photoisomerization of the azo functional groups was studied by UV-Vis absorption spectroscopy. The results suggest the photomagnetic effects are due to structural changes driven by the photoisomerization of the azo functional groups, leading to a different strength of magnetic exchange coupling. The second focus of this work is to characterize the depth-resolved magnetization of thin films of the organic-based magnet, V[TCNE]x~2. Practical application of this material has been realized in spintronic devices, thus it is important to fully understand the chemical and magnetic properties throughout the films. Different thicknesses of V[TCNE]x~2 films prepared by chemical vapor deposition (CVD) were studied. Their bulk magnetizations show a thickness dependence at low magnetic field, suggesting stronger random magnetic anisotropy is present in the thicker film; however, this phenomenon disappears at sufficiently high fields. The depth profiles from polarized neutron reflectivity studies exhibit two sublayers in V[TCNE]x~2 film, which is ascribed to partial oxidation occurring in the top portion of the layer. Detailed analysis suggests the chemical and magnetic properties of V[TCNE]x~2 are homogeneous throughout the thickness of the film if there is no oxygen contamination.
Advisors/Committee Members: Epstein, Arthur.
Subjects: Chemistry
Keywords: organic-based magnet; photoinduced magnetism; polarized neutron reflectivity
More Like This
3.
Chen, Feng.
Mixed quantum/classical dynamics of photodissociation of H2O and Ar-H2O .
Degree: PhD, Chemical Physics, 2004, Ohio State University
► We present multiple configurational mixed quantum/classical studies of the photodissociation dynamics of…
(more)
▼ We present multiple configurational mixed quantum/classical studies of the photodissociation dynamics of H2O (Ã←X̃) and Ar-H2O (Ã←X̃). In this approach, the dynamics of the argon atom and one of the hydrogen atoms are treated classically, while the dynamics of the remaining OH molecule are treated quantum mechanically. The quantum subsystem is further divided into two or more coupled contributions and separately propagated in the classical trajectory dynamics to obtain accurate results. The accuracy of the multiple configurational mixed quantum/classical method is tested against an exact quantum treatment of H2O photodissociation on the excited state. We obtained good agreement between the OH rotational distributions and photodissociation cross section obtained by the two approaches. Vibrationally mediated photodissociation dynamics of Ar-H2O has been studied by this method and compared with experimental results. By comparing the rotational distribution of the OH product obtained from photodissociation of Ar-H2O and H2O , the influence of the Ar atom on the photolysis process can be regarded as a spectator in intracluster collision. The simulation provides an insight to the dynamics of photodissociation in clusters.
Advisors/Committee Members: McCoy, Anne B.
Subjects: Chemistry, Physical
Keywords: mixed quantum/classical method; photodissociation
More Like This
4.
Chen, Ming-Wei.
Laser Spectroscopy Studying Organic and Inorganic Intermediates in The Atmospheric Oxidation Process.
Degree: PhD, Chemical Physics, 2011, Ohio State University
► Laser spectroscopy is a powerful tool to study the structure and photochemistry…
(more)
▼ Laser spectroscopy is a powerful tool to study the structure and photochemistry of molecules at selected electronic states. Under jet-cooled conditions, the rotational spectrum can be simplified with less congestion on the rotational contour owing to the low J population on the ground electronic state. Laser induced fluorescence (LIF), stimulated emission pumping (SEP), and cavity ringdown spectroscopy (CRDS) apparatuses are used to measure the methoxy(CH3O·), β-hydroxyethylperoxy (HOC2H4OO·) and nitrate (NO3·) radicals. The novel laser spectroscopy apparatuses are designed for the direct measurement to the forbidden electronic state attributed to the selection rules or low absorption cross section. The spectroscopic analysis applies the least-square fitting to determine the molecular parameters in Hamiltonians as well as the vibronic coupling induced distortion of molecular structure. Furthermore, in the collaboration with Dr. W. Leo Meerts (Radboud University, The Netherlands), the quantum mechanical model is also adapted to the evolutionary algorithm to investigate the biological evaluation on spectrum simulation.The ~A2A1-~X2E3/2 and ~X2E1/2-~A2A1 electronic transitions of methoxy and all four deuterium isotopologues are measured with a LIF/SEP apparatus that is both high-resolution (Δν ∼ 250 MHz) and and high-accuracy (Δσ ∼ 50 MHz). Since the ~X2E1/2 state is not thermally populated in a jet-cooled environment, the complementary SEP experiment directly interrogates the ~X2E1/2 level of methoxy by depleting the fluorescence from the ~A2A1 state. The global analysis of the microwave, LIF, and SEP data breaks correlations in the microwave data and provides better determinations for the ~X and ~A states′ parameters. The jet-cooled ~A-~X origin band spectra of 1G2G3 conformer of β-hydroxyethylperoxy have been recorded by a CRDS appratus with a laser source linewidth ∼ 70 MHz in the near IR region. The spectra of four deuterium-substituted isotopologues have been analyzed and successfully simulated with an evolutionary algorithm, confirming the cyclic structure of the molecule responsible for the observed origin band. The broadened l inewidth on the absorption spectrum (Δν > 2 GHz) is due to the shortened lifetime of the ~A state attributed to excitation induced hydrogen transfer from the OH to the OO site of the molecule. The vibronic spectra of nitrate radical are recorded with the CRDS apparatus under jet-cooled conditions for the ~A2E′′-~X2A2′ electronic transition. The rotationally resolved 210, 410, and 420 bands have been recorded for studying the perpendicular (ν2) and parallel (ν4) band types. In addition, the vibronically forbidden 000 band is also found to be different from either perpendicular or parallel band type and is likely due to the magnetic dipole transition. Ground state combination differences are used to analyze the vibronic bands, and the preliminary assignments are utilized for the comprehensive understanding of the NO3 structure in the ~A state.
Advisors/Committee Members: Miller, Terry.
Subjects: Physical Chemistry
Keywords: Spectroscopy; high-resolution; Laser Induced Fluorescence; LIF; Stimulated Emission Pumping; SEP; Cavity Ringdown Spectroscopy; CRDS; methoxy; CH3O; beta-hydroxyethylperoxy; HEP; nitrate; NO3; jet-cooled; gas-phase; Jahn-Teller effect
More Like This
6.
Fletcher, Kerra Rose.
Low field modulation of complex species.
Degree: MS, Chemical Physics, 2008, Ohio State University
► One of the fundamental problems in the analysis of complex molecules is…
(more)
▼ One of the fundamental problems in the analysis of complex molecules is it dense rotational spectra. Simplifying spectra whose transitions could be accurately predicted would create a powerful analytical tool with useful applications. Modulation by means of an electric field has proven a useful tool for determining the dipole moment of a molecule. Stark modulation can also be used to simplify the dense spectra of complex molecules at high J values. Modulation makes it possible to separate the absorptions from the otherwise dense background. The distinction between unmodulated and modulated lines is governed by the rotational energy levels of the molecule. Employing the FASSSTER system, Stark modulation was achieved for various molecules, including acetonitrile and ethyl formate. Acetonitrile, a symmetric rotor, demonstrates first-order effects. Ethyl formate, a prolate asymmetric rotor, exhibits first- and second- order effects, as well as unmodulated transitions.
Advisors/Committee Members: De Lucia, Frank.
Subjects: Chemistry, Physical
Keywords: Stark modulation, FASSSTER, ethyl formate
More Like This
7.
Giardina, Matthew.
THE DEVELOPMENT AND CHARACTERIZATION OF LOW-TEMPERATURE GLASSY CARBON FILMS FOR SOLID PHASE MICROEXTRACTION.
Degree: PhD, Chemical Physics, 2002, Ohio State University
► Solid phase microextraction (SPME) has become an invaluable tool for the rapid…
(more)
▼ Solid phase microextraction (SPME) has become an invaluable tool for the rapid extraction and analysis of trace organic compounds. The unique characteristics of low temperature glassy carbon (LTGC) make it particularly well suited as a sorbent coating for SPME and as a result, its properties are quite distinct among the compendium of available phases. To evaluate this novel application of LTGC, a detailed investigation into the preparation, characterization and application of LTGC coatings for SPME was carried out. To apply LTGC in films in SPME, a suitable substrate had to be developed. This was accomplished using a sol-gel immobilization process, in which porous silica particles were attached to stainless steel fibers using a sol-gel binder. The inclusion of porous silica particles allowed the LTGC films to be applied over a large surface area. The LTGC films were prepared by first coating the porous silica with a poly(phenylene diethynyl) oligomer precursor and then heating the coated silica to final temperatures between 300 and 1000 degrees celcius. The extraction characteristics of a silicon and fluorine containing LTGC were investigated for a number of solute systems and carbon processing arrangements. The data gathered from these experiments indicate that extractions with LTGC are highly dependent on dispersive interactions between the solute and the carbon surface. The greatest predictor of selectivity was the based upon the cross-sectional surface area and polarizability of the solutes. It was also determined that the selectivity and absorptive strength of the carbon increased as a function of processing temperature in accordance with the rearrangement of the carbon bonds during the formation of the microcrystaline glassy-carbon structure. Comparing the silicon and fluorine LTGC, it was found that the fluorine LTGC formed the graphitic structure sooner and more completely than the silicon LTGC during thermal processing. In addition to fundamental investigations, a series of applications was developed for LTGC-SPME fibers. These applications included the extraction of alga metabolites from water; simulated breath volatiles associated with lung cancer; and simulated sulfide compounds released from brassica plant tissue. In all cases, the LTGC-SPME provided unique extraction properties compared the commercial SPME phases.
Advisors/Committee Members: Olesik, Susan.
Subjects: Chemistry, Analytical
Keywords: Solid phase microextraction; Low temperature glassy carbon; Extraction; Separation; Chromatography
More Like This
8.
Graff, David L.
Sub-millimeter Spectroscopy at the Confusion Limit.
Degree: PhD, Chemical Physics, 2010, Ohio State University
► Interest in SMM/THz spectroscopy is partly driven by its potential as an…
(more)
▼ Interest in SMM/THz spectroscopy is partly driven by its potential as an analytic method. Briefly, rotational spectroscopy in the SMM/THz is a high resolution technique capable of absolute specificity due to the fact that each molecule has a unique rotational spectrum (fingerprint) that for most molecules of interest fills only a small portion of the available resolution elements (< 0.1%). Further, because the field has traditionally used low-power devices, very sensitive detector systems are available for making trace measurements. We have designed and built a solid-state Multi-Purpose Spectrometer based on recently available broadband amplifier/multiplier chains and new X-Band electronic synthesizers. The frequency precision and agility of the synthesizers allow the Multi-Purpose Spectrometer to implement many analytic strategies, including fast-scanning, frequency modulation, Stark modulation and cavity absorption without changes to the spectrometer hardware. The Multi-Purpose Spectrometer was built to investigate the effects of making analytical measurements on larger molecules that contain highly congested spectra (> 1000 lines/GHz). At question is to what extent increasing spectral congestion will impact the ability to identify trace elements of a gas mixture in an otherwise congested spectrum. We report our tests of the effectiveness of the frequency modulation technique in congested environments and whether Stark modulation and cavity absorption techniques are effective alternatives to frequency modulation in these environments. To this end, the frequency modulation spectrum of a series of large, planar molecules based on the benzonitrile backbone (benzonitrile, all six difluorobenzonitriles and pentafluorobenzonitrile) have been measured between 180 - 270 GHz with an FM spectrometer and the ground-state spectra of all but pentafluorobenzonitrile were assigned, followed by companion measurements of some of the molecules with the Stark modulation and cavity absorption techniques. We found that the “Confusion Limit” was reached as the rotational constant C approached 1000 MHz and the percentage of resolution elements occupied by lines exceeded 20%. In this “limit”, the baseline was indistinguishable from weak, overlapping absorption features, limiting the sensitivity to trace gas absorption in an otherwise pure sample. Further, as the rotational constant C fell below 800 MHz, over 50% of the resolution elements were filled, leading to significant feature overlap and a breakdown in the FM technique across small portions of the spectrum. Stark modulation is capable of reducing spectral congestion by selectively modulating only the so-called “prolate-degenerate” transitions in a molecule with no c-type dipole moment. Reduction for even moderately oblate asymmetric rotors is well above 50%. Also, we have identified a new fingerprint based on the response of near-prolate asymmetry doublets to varying electric field strength. Cavity absorption proved capable of making measurements of the broad continuum absorption features of molecules at higher pressures without losing the spectral fingerprints of the strong ground-state spectral lines. In addition, it provides a convenient method for measuring the spectra of molecules limited by the vibrational partition function, as the cavity is sensitive to the integrated absorption of many weak lines from excited vibrational states.
Advisors/Committee Members: De Lucia, Frank C.
Subjects: Chemistry; Physics
Keywords: sub-millimeter spectroscopy; THz spectroscopy; benzonitrile; Stark modulation; cavity absorption
More Like This
9.
Heer, Joseph Michael.
FDTD Modeling of the Spectroscopy and Resonances of Thin Films and Particles on Plasmonic Nickel Mesh.
Degree: PhD, Chemical Physics, 2010, Ohio State University
► Infrared spectra of individual micron-scale particles can be measured accurately and inexpensively…
(more)
▼ Infrared spectra of individual micron-scale particles can be measured accurately and inexpensively by placing them in the holes of plasmonic nickel mesh. This thesis describes many aspects of modeling infrared spectra of particles and coating in or near the holes of nickel mesh using Finite-Difference-Time-Domain (FDTD) software. These aspects include: 1) Background information on surface plasmons and extraordinary transmission 2) Background information about modeling with FDTD systems. 3) Simple mesh models that predict plasmonic mesh spectra qualitatively. 4) More complex mesh models that take much longer but give quantitative results. 5) Important aspects about modeling peak splitting in plasmonic mesh. 6) Modeling plasmonic mesh with thin layers and coatings. 7) Modeling the spectra of individual particles on plasmonic mesh.
Advisors/Committee Members: Coe, James.
Subjects: Chemistry; Condensed Matter Physics
Keywords: FDTD; infrared; spectroscopy; surface plasmons; SPP; mesh; modeling; transmission resonance
More Like This
10.
Helmus, Jonathan Jaye.
Structure and Dynamics of the Y145Stop Variant of the Human Prion Protein Studied by Magic-Angle Spinning Solid State NMR.
Degree: PhD, Chemical Physics, 2011, Ohio State University
► Transmissible spongiform encephalopathies (TSEs), a group of neurodegenerative diseases including scrapie in…
(more)
▼ Transmissible spongiform encephalopathies (TSEs), a group of neurodegenerative diseases including scrapie in sheep, bovine spongiform encephalopathy in cattle, and Creutzfeldt-Jakob disease in humans, are caused by the conversion of the monometic prion protein to highly ordered, amyloid aggregates. These amyloid aggregates are believed to be the infectious agent, accounting for the transmissibility of TSEs. In this work, we used solid state NMR methods to determine the structure and dynamic properties of the Y145Stop mutant of the human prion protein, huPrP23-144, in its fibril state. This variant is readily converted under physiologically relevant buffer conditions from soluble monomeric form to amyloid fibrils and provides an experimentally tractable model which reproduces in vitro some of the most fundamental aspects of prion propagation, including the phenomena of 'species barrier' and prion strains. Understanding the atomic level, three-dimensional structure and conformation dynamics of these fibrils is fundamental to understanding their functions in living organisms, and may in time lead to the development of effective medical treatments for TSEs and other amyloidal diseases. The insoluble, non-crystalline nature of amyloid fibrils makes studying these molecules difficult by traditional high-resolution structural techniques, however solid state NMR has been used in the past decade to study a number of proteins in their amyloid state. In this work, we apply the solid state NMR techniques used in these studies as well as a number of experiments designed by our group to study huPrP23-144 fibrils. Surprisingly, our initial studies revealed that huPrP23-144 fibrils contains a highly compact, relatively rigid and β-sheet-rich core region of ~30 amino acids located near the C-terminus. Concurrently, the remaining residues, corresponding primarily to the large N-terminal domain, exhibit significant conformational flexibility within the fibril lattice. An analysis of the conformational flexibility of huPrP23-144 fibrils by detecting directly, at ambient conditions, the highly dynamic segments using J-coupling based MAS SSNMR methods, found the presence of all amino acid types outside the core region of fibrils. Experiments which probed the molecular motions occurring on the NMR timescale within the relatively rigid amyloid core domain, using site-resolved SSNMR measurements of backbone dipolar order parameters, found little variation on the sub-μs timescale. Similar experiments which examined the transverse spin relaxation rate constants found significant variations from motions on the μs-ms timescale which likely underlie the large variation in peak intensities seen in earlier 3D correlation experiments. Using a series of 15N-13C correlation experiments on uniform, dilute and mixed isotopically labeled samples, huPrP23-144 molecules were found to align in-register and parallel to form fibrils with an approximate inter-fibril distance of 4.4 angstrom. These experiments also detected the presence of a number of long-range structural restraints which were verified and expanded in a series of time resolved correlation experiment to provide a number of 15N-13C and 13C-13C distance restraints. When combined with the results from three dipole correlation experiments, which provide restraints on the protein backbone torsion angles, an atomic level structural model of huPrP23-144 amyloid fibrils is beginning to form.
Advisors/Committee Members: Jaroniec, Christopher.
Subjects: Biochemistry; Chemistry; Physical Chemistry; Physics
Keywords: Sold State NMR; NMR; protein NMR; prion protein, amyloid fibril; amyloid structure; prion structrure; Transmissible spongiform encephalopathies
More Like This
11.
Just, Gabriel Michel Paul.
High Resolution Cavity Ringdown Spectroscopy of the A - X Electronic Transition of Alkyl Peroxy Radicals.
Degree: PhD, Chemical Physics, 2009, Ohio State University
► Alkyl peroxy radicals (RO2) are examples of reactive intermediates involved in the…
(more)
▼ Alkyl peroxy radicals (RO2) are examples of reactive intermediates involved in the oxidation of organic molecules. This chemistry plays a key role in combustion as well as in tropospheric chemistry. These reactions are typically very complex involving thousands of elementary steps with a corresponding number of chemical intermediates. Hence, spectroscopic diagnostic based upon fully understood spectra is a key to monitor such reactions and understand their mechanism. Over the last few years, our laboratory has investigated these peroxy radicals via their A-X electronic transition which lies in the near infrared. Due to the relative weakness of this transition, we use cavity ringdown spectroscopy (CRDS) to detect these radicals which is known to be a very sensitive technique. We have obtain high resolution jet-cooled CRDS spectra of several of these alkyl peroxy radical at a rotational temperature of 15 K. This dissertation will focus on the numerous species that we observed and analyzed using our high resolution setup and an Evolutionary Algorithm as well as the analysis of the methyl tunneling splitting of the methyl peroxy radical observed at room temperature and at 15 K.
Advisors/Committee Members: Miller, Terry.
Subjects: Chemistry
Keywords: High Resolution Cavity Ringdown Peroxy Radicals
More Like This
13.
Kuo, Jer-Lai.
Graph Invariants - A Tool to Analyze Hydrogen Bonding in Ice and Water Clusters.
Degree: PhD, Chemical Physics, 2003, Ohio State University
► We have studied a wide range of aqueous systems, from the order/disorder…
(more)
▼ We have studied a wide range of aqueous systems, from the order/disorder in the hydrogen bond network of ordinary ice, a fundamental problem in ice physics for over 70 years, to properties of water clusters. A common theoretical difficulty in these systems is the enormous number of hydrogen bond arrangements that must be considered in these systems, and for which no systematic treatment has been available. Our analytical method based on graph theory and the introduction of graph invariants provides a means for efficient and reliable analysis. Recent investigations of water clusters have demonstrated that graph invariants provide a powerful tool for capturing very complex behavior using only a small number of parameters, and some of our findings have uncovered unknown aspects of the behavior of water clusters. Applications of this analytic method provide insight into the nature of hydrogen bond disorder in ice, and impact our understanding of chemical reactions in water clusters important to environmental chemistry.
Advisors/Committee Members: Singer, Sherwin J.
Subjects: Physics, Molecular
Keywords: Hydrogen Bond; ice XI; water clusters; short H-bond; graph invariants; group theory
More Like This
14.
Liu, Jinjun.
Laser-induced fluorescence spectroscopy of the alkoxy radicals.
Degree: PhD, Chemical Physics, 2007, Ohio State University
► Laser-induced fluorescence (LIF) spectra of large primary and secondary straight-chain alkoxy radicals…
(more)
▼ Laser-induced fluorescence (LIF) spectra of large primary and secondary straight-chain alkoxy radicals and cyclohexoxy (c-C6H11O) were recorded under jet-cooled conditions (T~1K). For 1-hexoxy (1-C6H13O), 1-heptoxy(1-C7H15O) and 2-butoxy (2-C4H9O), rotational constants for both the ground electronic (X) state and the second excited (B) state, and components of the spin-rotational tensor for the X state were obtained by an analysis of the resolved rotational and fine structure of the vibronic bands. Comparing these experimental results with quantum chemistry calculations permitted unambiguous conformational and vibrational assignments for the bands. Such techniques have been extended to larger straight-chain alkoxy radicals. A high-resolution LIF apparatus has been improved by the addition of a high-accuracy calibration system. With this apparatus we have studied the methoxy radical (CH3O) and its deuterated isotopomers (CH2DO, CHD2O and CD3O). A spectral resolution (Full Width at Half Maximum, FWHM) of ~250MHz in the UV spectral region was achieved and individual lines have been measured with an absolute accuracy (one standard deviation) ~50MHz at a frequency of ~109MHz, i.e., ~0.05ppm. Vibronic bands of different rotational types of transitions from the lower-energy spin-orbit component of the ground electronic state (X^2E_{3/2}) to the first excited state(A^2A_1) have been recorded. A global fitting combining the LIF and previously observed microwave and stimulated emission pumping (SEP) spectra, which involves the higher-energy spin-orbit component of the ground electronic state (X^2E_{1/2}), to a rotational and fine structure Hamiltonian has been achieved. All of the above data reveal the structure and properties of the alkoxy radicals, which are important intermediate species in the oxidation of hydrocarbons, a reaction that is critical in both combustion and atmospheric chemistry. The spectroscopy is a prerequisite for subsequent dynamic studies. Our work is also of special theoretical interest due to the fact that methoxy radical provides a benchmark case of the Jahn-Teller effect coupled with spin-orbit interaction, giving rise to a potential energy surface which stringently tests modern ab initio calculations.
Advisors/Committee Members: Miller, Terry A.
Keywords: laser-induced fluorescence (LIF); high-resolution; high-accuracy; alkoxy radicals; methoxy radical; deuterated isotopomers; Jahn-Teller effect
More Like This
15.
López, José G.
Theoretical studies of the dynamics and spectroscopy of weakly bound systems.
Degree: PhD, Chemical Physics, 2005, Ohio State University
► In this thesis, the results of a theoretical investigation of the dynamics…
(more)
▼ In this thesis, the results of a theoretical investigation of the dynamics and spectroscopy of two weakly bound systems are reported. Classical trajectory simulations are used to study the three-dimensional collision dynamics of Ne + Ar2. From an analysis of the neon kinetic energy distributions after the collision of a neon atom with the argon dimer, it is found that sampling the initial conditions from a quantum phase space distribution given by the Wigner function provides a straightforward way to incorporate the most important quantum mechanical effects in simulations of collisions involving very cold weakly bound complexes. The effects of solvation on the transition state region of the I+HI reaction are investigated using classical trajectory simulations of the dynamics of ArnIHI and time-independent quantum simulations of the photoelectron spectra of ArnIHI- with n = 0 to 20. Excellent agreement between the stepwise spectral shifts measured from the experimental photoelectron spectra of ArnIHI- and those calculated in this work is found. Longer lifetimes of the IHI complex, increased trapping of the hydrogen atom near the center of the complex, and increasing energy transfer between the hydrogen atom and the argon and iodine atoms are also observed as the number of argon atoms is increased. It is also found that the I-I motion mainly affects the v3' spectrum features, while the progressions associated with hindered rotor transitions are barely affected. Finally, comparisons between the experimental PE spectra of ArnIHI- and those obtained by using an adiabatic approximation with n > 0 showed that this approximation might lead to an underestimation of the intensities of the peaks near v3' = 2 and 4 and therefore inclusion of non-adiabatic effects might be required for the calculations of these intensities.
Advisors/Committee Members: McCoy, Anne B.
Subjects: Chemistry, Physical
Keywords: Weakly Bound Complexes; Molecular and Atomic Clusters; Transition State; Photoelectron Spectroscopy; Collision Dynamics; Classical Trajectory Simulations; Quantum Calculations
More Like This
16.
Melnik, Dmitry Georgievich.
Submillimeter wave absorption spectroscopy in the free jet environment.
Degree: PhD, Chemical Physics, 2003, Ohio State University
► The frequency of a vibrational mode depends on the reduced mass characteristic…
(more)
▼ The frequency of a vibrational mode depends on the reduced mass characteristic of the mode, and the restoring force, driving the molecule towards the equlibrium configuration. If such reduced mass is large and/or restoring force is small, the eigenfrequency of the mode becomes low. In certain cases, the transition frequencies of vibration modes in question lies in sub-teraherz region. Vibrational spectroscopy of such low frequency vibrational modes provides a unique opportunity to explore the details of the potential surfaces of the molecules and intermolecular interaction between moieties comprising weakly bound complexes, such as van der Waals molecule. For the purpose of searching for and studying, of such low frequency vibrational modes, a new spectrometer operating in the submillimeter wave region has been designed. The apparatus combines a previously developed FASSST (FAst Scan Submillimeter wave Spectroscopic Technique) technique with a pulsed supersonic jet sample. We have demonstrated that the apparatus is capable of performing the search for the previously unobserved weak transitions by observation of the transitions in Ar-CO and low abundance isotopomers of CO. A series of van der Waals complexes Rg-ND3 (Rg = Ne, Ar, Kr) have been studied using the newly developed technique. In particular, a vibrational-torsional-rotation band Σ 00 - Π 10 has been observed in all of the complexes involved, including 2 isotopomers of Ne-ND3 and 4 isotopomers of Kr-ND3. The two nuclear spin components corresponding to the different inversion states of ammonia, were observed, and the effect of complexation on the inversional motion of ammonia has been studied. Another kind of a large amplitude motion, pseudorotation, in heterocyclic five-membered rings, such as tetrahydrofuran (THF) and 1,3-dioxolane (DOX), has been studied. One pseudororotational band in THF and two bands in DOX were observed, which have not been reported previously. The observation of the new bands in both molecules allowed us to determine the symmetries and the energies of the lowest pseudorotational states, and to derive the functional form of the barrier to pseudorotation. An analytical and computational formalism for the description of lightly hindered pseudorotation characteristics has been developed. A discussion of the analytical capabilities, and potential further improvements to the experimental technique is given.
Advisors/Committee Members: Miller, Terry A.
Keywords: FASSST; Tetrahydrofuran; 1,3-dioxolane; THF; DOX; ammonia complex; van der Waals; pseudorotation; hindered rotation
More Like This
17.
Oelgoetz, Justin Ryan.
Atomic data and plasma spectroscopy.
Degree: PhD, Chemical Physics, 2006, Ohio State University
► The spectroscopy of plasmas is one of the principal methods by which…
(more)
▼ The spectroscopy of plasmas is one of the principal methods by which astronomers interrogate distant objects. Many of these plasmas cannot be created in the lab, and as such must be studied using computational tools. This document sets forth a new, generic, methodology and computer program, the General Spectral Modeling (GSM) code for the study of such plasmas. GSM allows for diverse types of data to be joined into a common model that is not tied to a specific element, ionization stage, or set of conditions. GSM is then used to explore a number of conditions of interest in the X ray spectroscopy of helium-like ions in astrophysics, and develop diagnostics for the conditions of those plasmas by looking at ratios of key spectral features. It is also used to look at a higher density system more along the lines of what one might see in a laboratory plasma. This document also discusses how the data in these models were calculated from ab initio quantum mechanics, as well as attempts to advance the field of atomic data calculation through work with the R-Matrix II method.
Advisors/Committee Members: Pradhan, Anil K.
Subjects: Physics, Atomic
Keywords: X-Ray Spectroscopy; Plasma Spectroscopy; Atomic Spectroscopy; Spectroscopy; Atomic Physics; Fe XXV; Ni XXVII; Ca XIX; X-Ray Astronomy; he-like ions; GSM; General Spectral Modeling
More Like This
18.
Oesterling, Lee Clifford.
Millimeter-Wave Time-Resolved Studies of Chemical and Physical Interactions Between Molecular Ions, Neutrals, and Electrons.
Degree: PhD, Chemical Physics, 2009, Ohio State University
► We constructed a novel spectroscopic system to study rotationally inelastic collisions involving…
(more)
▼ We constructed a novel spectroscopic system to study rotationally inelastic collisions involving truly thermal molecular ions at low temperatures. This system utilizes magnetic confinement to generate abundant concentrations of ions and time-resolved double resonance (pump-probe) techniques to study rotational energy transfer. With this system, we studied chemical and physical processes involving HCO+ and CO+ molecular ions in gas mixtures containing hydrogen and carbon monoxide. We measured the relaxation cross section for the J=2 state of HCO+ in collisions with normal hydrogen at temperatures around 40 K and 77 K. The cross sections at the lower temperature are slightly below those predicted by Langevin theory, while those at the higher temperature are in good agreement with this theory. This dissertation discusses the discrepancy of the acquired data with Langevin theory at lower temperatures. We also performed rotational energy level spectroscopic studies of the methyl formate and symmetric mono-deuterated methyl formate molecules. We developed a rho-axis method (RAM) analysis to accurately model the rotational-torsional spectrum for the ground torsional state. In this work, we report the first measurement and analysis of millimeter-wave (mmw) and submillimeter-wave (submmw) rotational-torsional transitions for mono-deuterated methyl formate. Additionally, we extended the spectral analysis of methyl formate to higher angular momentum and higher spectral frequencies than previously reported.
Advisors/Committee Members: De Lucia, Frank.
Subjects: Physics
Keywords: time-resolved spectroscopy, molecular ions, rotational energy transfer, millimeter-wave
More Like This
19.
Park, In Hee.
Dark cloud modeling for the ortho-to-para abundance ratio of the cyclic C 3 H 2.
Degree: MS, Chemical Physics, 2005, Ohio State University
► We present the first attempt to model the ortho-to-para abundance ratio (hereafter…
(more)
▼ We present the first attempt to model the ortho-to-para abundance ratio (hereafter o/p ) of c-C 3 H 2 so as to reproduce its observed ratio in cold dense clouds. According to observations for TMC-1 (a quiescent, starless core), TMC-1C (a prestellar core) and L1527 (a protostellar core), the o/p -C 3 H 2 ratio is 2.4 - 2.7, a value which is only slightly lower than the statistical ratio of 3 pertaining to high temperature equilibrium. In order to model the ortho-to-para abundance ratio, we used a large network of chemical reactions augmented by reactions that specifically consider the formation and depletion of ortho and para forms of the molecules c-C 3 H 2 and c-C 3 H 3 + . The reaction branchfractions were determined by a variety of considerations. We then investigated the sensitivity of the calculated ortho-to-para ratio for c-C 3 H 2 to a number of factors such as time, density, elemental C/O ratio, the depletion of metals from the gas, and the cosmic ray ionization rate. While these parameters can affect the calculated ratio, the major factor appears to be the choice of branching fractions for the neutral products of the C 3 H 3 + + e - dissociative recombination reaction. In particular, in order to reproduce the o/p -C 3 H 2 ratio, it is necessary that the product channel C 3 H 2 + H be the dominant one.
Advisors/Committee Members: Herbst, Eric.
Keywords: Chemical modeling; Molecular abundances; Molecular processes
More Like This
20.
Park, In-Hee.
Computational Simulations of Protein-Ligand Molecular Recognition via Enhanced Samplings, Free Energy Calculations and Applications to Structure-Based Drug Design.
Degree: PhD, Chemical Physics, 2010, Ohio State University
► The objective of this dissertation is to understand the underlying intermolecular interactions…
(more)
▼ The objective of this dissertation is to understand the underlying intermolecular interactions between disease-causing proteins and anti-disease small-molecule drugs (also known as ligands) through computational methodologies. The insight gained into protein-ligand molecular recognition in terms of structural and energetic complementarities can be rationally utilized for efficient drug discovery, i.e., structure-based drug design (SBDD), to treat diseases caused by specific proteins, including cancers caused by dimerization of survivin (Chapter 2) and of STAT3 (Chapters 4 and 5), and a degenerative, cataract-inducing eye disease caused by misfolding of gammaS-crystallin (Chapter 3). Protein structures are not static in the body; thus, a single structure cannot fully represent a protein's characteristics. Proteins in aqueous environments have ensemble structures that range from small-scale variations, such as ligand-induced conformational changes (Chapter 2), to large-scale variations, such as protein unfolding and denaturation (Chapter 3). A non-Boltzmann ensemble distribution ('Generalized Boltzmann distribution') can be realized through enhanced sampling methods which help to overcome the pre-existing free energy barriers along the potential energy surface, allowing a wide range of protein structure conformations to be sampled. The extraction of an essential reaction coordinate that constitutes a protein reaction pathway, followed by the construction of a Potential of Mean Force (PMF: the free energy landscape as a function of a selected reaction coordinate), can be utilized for conformational mapping to elucidate the protein's transition structure and thus understand its mechanism. For candidate ligands to become effective drugs, they should bind to specific protein binding sites with sufficient affinity while controlling the biological reactions of interest. Therefore, estimating the binding energy of a ligand is a crucial metric in assessing a drug's potency. Furthermore, the predicted binding energy should be sufficiently accurate to discriminate the subtle differences associated with its characteristic specificity among similar candidate ligands, as medicinal chemistry usually deals with libraries that contain a large number of chemical compounds. The characterization of the intermolecular forces required for protein-ligand recognition via classical force fields (Chapter 4) and quantum mechanical force fields (Chapter 5) by extracting amino acid residue-by-residue contributions to the ligand binding energy has enriched the quantitative information that can be used for SBDD.
Advisors/Committee Members: Li, Chenglong.
Subjects: Biomedical research; Biophysics; Chemistry
Keywords: enhanced sampling; free energy calculation; structure-based drug design; ligand-induced-fit simulation; survivin
More Like This
21.
Quan, Donghui.
Chemical Modeling of Interstellar Molecules in Dense Cores.
Degree: PhD, Chemical Physics, 2009, Ohio State University
► There are billions of stars in our galaxy, the Milky Way Galaxy.…
(more)
▼ There are billions of stars in our galaxy, the Milky Way Galaxy. In between the stars is where the so-called “interstellar medium” locates. The majority of the mass of interstellar medium is clumped into interstellar clouds, in which cold and hot dense cores exist. Despite of the extremely low densities and low temperatures of the dense cores, over one hundred molecules have been found in these sources. This makes the field of astrochemistry vivid. Chemical modeling plays very important roles to understand the mechanism of formation and destruction of interstellar molecules. In this thesis, chemical kinetics models of different types were applied: in Chapter 4, pure gas phase models were used for seven newly detected or confirmed molecules by the Green Bank Telescope; in Chapter 5, the potential reason of non-detection of O2 was explored; in Chapter 6, the mysterious behavior of CHNO and CHNS isomers were studied by gas-grain models. In addition, effects of varying rate coefficients to the models are also discussed in Chapter 3 and 7.
Advisors/Committee Members: HERBST, ERIC.
Keywords: Modeling Astrochemistry Astrophysics Interstellar Medium
More Like This
22.
Ronningen, Theodore J.
Low temperature helium pressure broadening of HCN.
Degree: PhD, Chemical Physics, 2005, Ohio State University
► We measured the helium induced pressure broadening and shifting of the distinct…
(more)
▼ We measured the helium induced pressure broadening and shifting of the distinct hyperfine components of the j = 1 ← 0 and j = 2 ← 1 transitions of HC14N at temperatures between 1.3 and 18 K. The HCN molecules were cooled to these temperatures using the collisional cooling technique. As a test that this cooling technique was generating the cold samples expected, we measured the Doppler contribution to the spectral lines, and these measurements confirmed that the molecules were at the same temperature as the walls of the spectroscopic cell. We observed that the hyperfine components of the 2 ← 1 transition have distinct broadening coefficients that differ from one another by as much as 5%. The measured differences are in reasonable agreement with theoretical predictions. We also performed molecular scattering calculations, using three proposed He-HCN potential energy surfaces, in order to compare our pressure broadening and shifting results with theoretical predictions. The predictions were within a few standard deviations near 18 K, but at the lowest experimental temperatures the predictions were many standard deviations larger than the measured values. This discrepancy is similar to a discrepancy found in two previous low temperature pressure broadening studies, and this dissertation discusses possible experimental and theoretical origins for this persistent discrepancy.
Advisors/Committee Members: De Lucia, Frank C.
Keywords: pressure broadening; molecular spectroscopy; millimeter-wave spectroscopy; spectroscopic line shapes
More Like This
23.
Sanzenbacher, Lindsay M.
Raman Spectroscopic Studies of Single Crystal Diamond.
Degree: MS, Chemical Physics, 2011, Ohio State University
► Current research in the field of quantum computing seeks to find suitable…
(more)
▼ Current research in the field of quantum computing seeks to find suitable materials and systems that meet the criteria to be used as quantum bits, or qubits. Carbon has many properties that make it an ideal host lattice for such systems, and already some defect centers, most notably the nitrogen-vacancy (NV) center, have been identified as good candidates for quantum computing applications. Raman spectroscopy, known to provide a good measure of the purity of synthesized diamond films, was used to characterize single crystal diamond samples containing different types of defects and impurities. Spectra collected at 785 nm excitation displayed additional peaks that are thought to be a result of resonant enhancement of single defect states in the diamond sample. Further characterization is needed to identify the specific origin of each peak, but these results indicate that Raman spectroscopy holds promise as a method to identify and measure individual defect states in diamond.
Advisors/Committee Members: Gupta, Jay.
Subjects: Condensed Matter Physics; Materials Science; Physical Chemistry
Keywords: Raman spectroscopy; diamond
More Like This
24.
Saprigin, Alexey V.
Optical studies of conducting polymers in metallic and semiconducting doped states.
Degree: PhD, Chemical Physics, 2001, Ohio State University
► A study of electromagnetic response was performed at direct current (DC), microwave…
(more)
▼ A study of electromagnetic response was performed at direct current (DC), microwave (6.5 GHz) and optical (15-40,000 cm-1) frequencies on poly(3,4-alkylenedi-oxythiophenes) (PADOTs) doped with various dopants near the insulator-metal transition together with structural studies (X-ray diffraction). We find these materials to be inhomogeneous, i.e. to have well defined crystalline regions within amorphous media. The transport measurements indicate that the properties of PADOTs vary from insulating to metallic. The metallic state of PADOTs follows trends found previously for the metallic polyaniline and polypyrrole thus confirming the universality of the metallic state for conducting polymers. The features of this state are the positive temperature coefficient of reduced activation energy, negative dielectric response at mw and far infrared frequencies, unique frequency dependence of the dielectric function and optical conductivity. A chain-linked network of metallic grains model is used in the discussion of experimental results. Within this model the transport in metallic conducting polymers is described by three basic electronic processes: intragrain scattering, diffusive spreading within the grains and the resonance hopping between the grains. The latter process is responsible for the negative dielectric responce and very long relaxation times characteristic for the metallic state of the conducting polymers. To further probe the metallic state of conducting polymers the polarized optical together with microwave and DC conductivity studies on stretch oriented films of polyaniline were performed in directions parallel and perpendicular to the stretch orientation. The low energy (far infrared and microwave) dielectric response was found to be negative for both directions. Together with the positive temperature coefficient of the reduced activation energy observed for parallel and perpendicular directions this proves the metallic state in conducting polymers is three-dimensional. Also included in this thesis is the study of LiCl treated emeraldine base (EB) form of polyaniline. We find that Li+ dopes EB based on the observation of new electronic states in the bandgap and associated with them spins. However, even at the maximum doping level LiCl doped polyaniline is a strongly localized charged insulator, a conducting polymer in a doped semiconducting state. This conclusion is based on the low DC conductivity, low dielectric constant, rapid decrease of the oscillator strength to zero in the infrared, low magnetic susceptibility dominated by a weak Curie-like component, broad EPR linewidth and predominantly Gaussian lineshape of the EPR signal found for LiCl processed EB. The results for LiCl doped polyaniline are compared to other conjugated polymers in the semiconducting doped state. The strongly localized properties of LiCl doped EB are attributed to the formation of spinless defects such as bipolarons.
Advisors/Committee Members: Epstein, Arthur J.
More Like This
25.
Sioutis, Ilias.
Experimental and computational investigation of Jahn-Teller active and other molecules.
Degree: PhD, Chemical Physics, 2006, Ohio State University
► The electronic-structure characteristics and vibrational properties of Jahn-Teller active and other molecules…
(more)
▼ The electronic-structure characteristics and vibrational properties of Jahn-Teller active and other molecules are investigated using experimental and computational methods. The vibrational structures of 1-propoxy, 1-butoxy, 2-propoxy, and 2-butoxy radicals in their ground X and low-lying A electronic states are investigated using the laser excited, dispersed fluorescence spectroscopic technique. Analysis of the spectra yields the energy separations of the vibrationless levels of the X and A states as well as their vibrational frequencies. Extensive ab initio calculations were performed for the X and A states of the silver trimer with the express purpose of guiding the analysis of the experimentally observed A-X electronic spectrum. Vibrational frequencies of the silver trimer for both the X and A state are reported. Spectroscopically obtainable parameters describing the Jahn-Teller effect are calculated for the X and A states, and the X-A electronic spectrum is predicted. Following extensive parameter fitting, the absorption and emission spectra are simulated and the bands are assigned. Theoretical calculations are performed for the X and A states of the tropyl radical, and are used as an aid to the analysis of the experimentally observed A-X electronic spectrum. Spectroscopically obtainable parameters describing the Jahn-Teller effect are calculated for the X and A states. The X-A electronic spectrum is predicted. The experimental molecular parameters characterizing the Jahn-Teller interaction in the X and A states are compared to theoretical results. The interaction of decaborane with the iodide ion and the (isoelectronic) xenon atom is studied using a number of theoretical methods. All non-DFT and some DFT methods agree that the complex with the iodide ion is bound by charge-dipole electrostatic forces, charge- and dipole-induced-dipole forces, and dispersion forces while the compex with the xenon atom is bound by dipole-induced-dipole forces and dispersion forces.
Advisors/Committee Members: Miller, Terry A.
Subjects: Chemistry, Physical
More Like This
26.
Stakhursky, Vadim L.
Vibronic structure and rotational spectra of radicals in degenerate electronic state. Case of CH3 O and asymmetrically deuterated isotopomers (CHD2 O and CH2 DO).
Degree: PhD, Chemical Physics, 2005, Ohio State University
► Spin-vibronic structure in the ground electronic state of methoxy radical is investigated…
(more)
▼ Spin-vibronic structure in the ground electronic state of methoxy radical is investigated using dispersed florescence (DF) spectroscopic technique via laser excitation of the 315 1, 3161, 314 1 and 35 vibrational states in the excited electronic state and using the rotationally resolved, stimulated-emission-pumping (SEP) technique with the excitation of specific rotational levels in the 35 and 3141 vibrational states in the intermediate electronic state. A Hamiltonian is derived for the Jahn-Teller distorted state of methoxy. The potential energy surface is parameterized up to third order terms in nuclear coordinates. In addition, a semi-quantitative approach is developed to treat high order terms perturbationally. The extended potential was successfully implemented in SOCJT software (Jahn-Teller interaction with spin-orbit coupling) in order to simulate and fit the observed dispersed fluorescence spectra. Particular interest is paid to the vibronic quartet structure, assigned in this work to CH stretch fundamentals, and observed in DF through emission from the 3141 level. Unperturbed positions of the symmetric and asymmetric CH stretch fundamentals as well as the value of the coupling constant between them has been derived from the analysis of the band positions and intensities. Analysis of the SEP spectra is used to validate further the symmetry assignment of the lines observed in DF spectrum. In addition, microwave spectra of the methoxy isotopomers, CHD2O and CH2DO, in subterahertz frequency region are investigated. For CHD2O 14 rotational transitions are assigned and for CH2DO 20 rotational transitions are assigned and parameters of the introduced effective Hamiltonian are determined. A general high throughput spectra simulation and data analysis package, SpecView, has been developed and utilized in the analysis described above. The architecture of the program allows for modeling of the electronic, vibrational or microwave spectra of any molecular system. A number of models, describing a large variety of molecules, diatomic and polyatomic, are included in the standard distribution package. The main program engine encapsulates a large number of commonly used procedures used for the processing of experimental data and various tools for the output of the calculated structures.
Advisors/Committee Members: Miller, Terry A.
Subjects: Chemistry, Physical
Keywords: Hamiltonian; VIBRONIC; pdParam; methoxy; quantum numbers
More Like This
27.
Teeters-Kennedy, Shannon M.
Infrared Surface Plasmons in Double Stacked Nickel Microarrays: Lipid Bilayer Systems.
Degree: PhD, Chemical Physics, 2007, Ohio State University
► An individual nickel mesh with a hole-to-hole spacing of 12.7 microns exhibits…
(more)
▼ An individual nickel mesh with a hole-to-hole spacing of 12.7 microns exhibits extraordinary properties in the infrared region, i.e. it transmits more light than is incident upon the holes. This results from propagating surface plasmons which "carry" light incident upon the metal to a hole, allowing it to be reemitted as light on the back side of the mesh. When two such mesh are stacked with a subwavelength spacing, the transmission of the stack mimics that of the single mesh, but the propagating surface plasmons can couple between the meshes producing narrower resonances. Characterization of the resonances shows how they disperse as a function of angle and reveals a splitting of the dispersion curve in momentum space, resulting from the coupling between the front and back surfaces of each mesh and perhaps between the meshes. This coupling phenomenon will be useful for passing infrared radiation through nanospaces enclosed within the mesh stack. The increased transmission can be exploited by applying a molecular coating to the mesh. The unique properties of the mesh allow the coatings to be studied with increased absorptions, easing the observation of weaker vibrations. Both vapor and solution deposition methods have been studied, with the primary focus herein on lipid bilayer coatings made from solution. Based upon their simplicity and relative importance in membrane studies, three different lipids were chosen for observation in the mesh system individually, as well as in combination with each other or cholesterol, to look for changes in the spectrum indicating interaction between the molecules. In addition, gramicidin, an antibiotic peptide, was observed in a system with one of the lipids (dipalmitoylphosphatidylcholine) as a first approximation for protein interactions. Finally, two relatively simple microorganisms (Saccharomyces cervisiae - yeast- and Eschericia coli - E. coli) were observed on the mesh.
Advisors/Committee Members: Coe, James V.
Subjects: Chemistry, Physical
More Like This
28.
Williams, Shaun Michael.
Characteristics and applications of the infrared enhanced transmission of metallic subwavelength arrays.
Degree: PhD, Chemical Physics, 2006, Ohio State University
► Metal films that are periodically patterned exhibit striking optical properties when illuminated…
(more)
▼ Metal films that are periodically patterned exhibit striking optical properties when illuminated with light of wavelength near the periodicitiy of the film. Nickel mesh with holes spaced by 12.7μm show a higher fractional transmission than the fractional open area of the mesh. This effect is attributed to surface plasmons which allow light incident on one side of the metal mesh to be transmitted to the other side where it is released as light. The majority of surface plasmon studies up to this point have been conducted in the visible and ultraviolet. Due to the hole spacing of this mesh, the surface plasmon phenomenon is seen in the infrared. Since this work is done in a different region of the electromagnetic spectrum, determining how the surface plasmons behave in this region will aid the overall understanding and help improve the current theories describing surface plasmons. Coating the nickel mesh with other metals allows the effect of the metal on transmission to be studied. In the visible and ultraviolet the metal is predicted to have an impact on the surface plasmons characteristics. Coating the mesh with other metals also closes down the holes so the effect of changing the size of the holes can be studied further aiding in an understanding of the importance of hole size on the surface plasmons. This increased transmission has been used to study molecular species which are bound to the surface of the mesh. The reaction that converts methanol to formaldehyde has been studied. Due to the unique spectroscopic properties of the mesh, surface species exhibit increased spectroscopic aborptions. The absorptions are enhanced to such an extent that the reactants, products and the adsorbed methoxy radical intermediate have been observed with significant intensity.
Advisors/Committee Members: Coe, James V.
More Like This
29.
Zalyubovsky, Sergey J.
Near IR cavity ringdown spectroscopy of peroxy radicals.
Degree: PhD, Chemical Physics, 2004, Ohio State University
► A sensitive Cavity Ringdown Spectroscopy (CRDS) apparatus has been successfully developed to…
(more)
▼ A sensitive Cavity Ringdown Spectroscopy (CRDS) apparatus has been successfully developed to study reactive intermediates in the near IR region. Many interesting species can be observed in this chemical fingerprint spectral region. Peroxy radicals (RO2), a class of important intermediates in atmospheric chemistry and low temperature combustion, have been investigated via IR à – X̃ electronic transition. Moderate resolution (0.2 cm−1) absorption spectra of the near IR electronic transition have been obtained for several members of the alkyl peroxy radical family: methyl (CH3O2), ethyl (C2H5O2) and isopropyl (2-C3H7O2) peroxy. CRDS spectra of the acetyl peroxy radical (CH3C(O)O2), a key irritant in smog, has been investigated. A sharp, structured electronic spectrum of à – X̃ electronic transition for the fluorinated methyl peroxy (CF3O2) radical has been observed. Extensive ab initio calculations have been carried out to help assign spectral carrier, predict and analyze observed spectroscopic features such as rotational contours, vibrational hot bands and frequencies for the à state fundamental vibrations. Structured spectral signatures of the transition contain information sufficient to distinguish the detailed nature of the R group, even when they are quite similar, providing an opportunity to easily identify different peroxy radicals and develop species specific diagnostics. The absorption cross sections for several peroxy radicals has been determined using CRDS observations and radical recombination kinetic measurements.
Advisors/Committee Members: Miller, Terry A.
Keywords: Peroxy Radicals; O2; Ringdown; CH3 O2; CF3 O2
More Like This
30.
Zhang, Luyuan.
Ultrafast Protein Hydration Dynamics Probed by Intrinsic Tryptophan.
Degree: PhD, Chemical Physics, 2010, Ohio State University
► Elucidation of water-protein interactions and dynamics is essential to the understanding of…
(more)
▼ Elucidation of water-protein interactions and dynamics is essential to the understanding of protein structure, dynamics and function. In this dissertation, we describe a novel methodology developed in our lab to probe the dynamics of water-protein interactions. The natural amino acid tryptophan is employed as an intrinsic optical probe. By integrating site-directed mutagenesis and state-of-the-art femtosecond laser spectroscopy, we are able to monitor the Stokes shift of tryptophan at any specific positions in proteins, one at a time, and the local hydration dynamics around tryptophan can be precisely determined. This dissertation presents several important protein systems we have investigated with this method. These include the membrane protein melittin, drug delivery protein human serum albumin, and the “hydrogen atom” of modern molecular biology, (apo)myoglobin. These protein systems have very different structures and biological functions. However, a robust double exponential hydration dynamics were observed in all these proteins, which represent two types of water relaxation processes. The first timescale is in several picoseconds and results from the initial local collective water network relaxation mainly through libration motions. The second time scale is in tens to hundreds of picoseconds and results from lateral hydration layer restructuring. The second process is strongly coupled with protein structure fluctuations and dynamic exchange between protein hydration water and bulk water. Both time scales are strongly correlated with protein architecture, such as secondary and tertiary structures, neighboring chemical identities, and protein structural flexibilities. These correlations were first evident in the systems of melittin and human serum albumin. Dynamics of hydration water gradually slows down as the melittin structure changes from random coil to α-helix to tetramer. While in human serum albumin, solvation dynamics change consistently during protein conformational transitions between multiple functional states. Then these correlations between hydration dynamics and protein properties were investigated in great detail in the protein apomyoglobin. Sixteen tryptophanyl mutants were designed to scan the protein surface. These tryptophans cover very different local protein environments, such as different secondary structures of loop or α-helix and different neighboring charged residue distributions. By changing pH to bring the protein to a folded native or a partially folded molten globular state, we were also able to investigate the global transitions of hydration dynamics during protein folding. The results provide clear and rich information of distinct behaviors of hydration water around various protein environments, revealing that hydration water is an integral part of proteins and directly “controls” their structure, dynamics and function.
Advisors/Committee Members: Zhong, Dongping.
Subjects: Biophysics
Keywords: Protein hydration dynamics, tryptophan, correlation
More Like This
[1] [2]
