Master of Science (MS), Wright State University, 2020, Physics

A recently constructed novel analytical tabletop terahertz (THz) chemical sensor capable of detecting a wide range of gases with high sensitivity and specificity was characterized to assess its performance over a range of operational parameters. The sensor was designed with an objective of quantifying composition of exhaled human breath, where target concentrations span part per trillion (ppt) to part per billion (ppb) level of dilutions. The sensor utilizes terahertz rotational spectroscopy of sampled gases for quantification of dilutions. The sensor occupies a volume of ~ 2 ft3 and incorporates a coiled absorption cell, thermal desorption tubes, and all necessary electronic components necessary for autonomous operation. Coiled absorption cell minimizes the sensor footprint while maintaining a large path length for sensitive spectral measurements. Preconcentration aides the detection of compounds by removing the background gases which would negatively affect the absorption signal if present during spectral analysis. Spectral parameters of the sensor were studied to optimize its sensitivity. Efficiencies of preconcentration over a range of gas sampling parameters were determined by comparing concentrations measured by the sensor to concentrations of a reference gas mixture. The sensor was characterized in its ability to detect acetaldehyde, acetone, ethanol, isoprene, and methanol – all known breath analytes. These gases were chosen for their range of volatility and absorption strength. Minimum detectable sample concentrations are well suited for breath sampling making this sensor a valuable new tool for environmental sensing and biosensing.

Committee: Ivan Medvedev Ph.D. (Advisor); Brent Foy Ph.D. (Committee Member); Jason Deibel Ph.D. (Committee Member) Subjects: Physics

PHD, Kent State University, 2016, College of Arts and Sciences / Department of Chemistry

High-resolution Fourier-transform rotational spectroscopy, combined with supersonic molecular beams, is an invaluable tool for studies of large amplitude motions in molecular systems, especially internal rotation tunneling of methyl groups. Methyl rotors are highly sensitive to local/non-local electronic environment and steric interactions. Therefore a systematic rotational-spectroscopic investigation of methyl rotors, along with the theoretical quantum chemical calculations, may reveal useful structural information of molecules and their weakly bonded van der Waals complexes. The dissertation includes rotational spectroscopic investigations of four sets of molecular systems: 1-7 methylindoles, conformers and argon complex of 2-phenylethyl methyl ether (2PME), normal/isotopologues and argon complex of guaiacol (2-methoxyphenol), and three structurally-isomeric methylstyrenes. Rotational spectra were recorded in the 10.5 – 22 GHz frequency range and transition frequencies were assigned to a suitable Hamiltonian, to determine the lowest energy structures, three-fold potential energy barriers to methyl internal rotation, and nitrogen-14 nuclear quadrupole coupling constants, where applicable.

Committee: Michael Tubergen Dr. (Advisor); Barry Dunietz Dr. (Committee Member); Songping Huang Dr. (Committee Member); John West Dr. (Committee Member); Spyridon Margetis Dr. (Committee Member) Subjects: Chemistry; Physical Chemistry

Doctor of Philosophy, The Ohio State University, 2014, Physics

THz systems are useful in a variety of fields such as astrophysics, analytical chemistry, security and communication. In this dissertation I present a computer simulation which allows evaluation of system performance, as well as the first submillimeter spectra of two molecular species: NdO and UO. The submillimeter spectra were recorded with a new high temperature spectroscopic system capable of temperatures of 2500 K while withstanding chemical and metallurgical attack. The simulation code addresses problems related to noise and nonlinear effects while maintaining a reasonable memory footprint and computational speed. It serves as a tool for system design and evaluation and bridges the information gap between technology developers and spectroscopists. The code is validated against experimental results from a well known ``standard'' spectrometer, as well as against fundamental theoretical results. It is then used to simulate a CMOS based system in development. The submillimeter spectra of NdO is presented and analyzed, building on the previous work in the optical region. The analysis results in improved spectroscopic constants, as well as constants for some never before measured states. In total, 1336 lines were recorded, of these, 643 were identified as belonging to series and 568 have vibronic assignments. The spectra also contain examples of resolved hyperfine structure for isotopes with nuclear spin, as well as examples of Ω doubling including one which resolved within the range of J recorded. Unlike NdO, UO has only one detectable isotope. As a result many fewer lines were recorded, a total of 274. However the analysis provided spectroscopic constants for four electronic states, including some vibrationally excited states which were previously unmeasured. In addition several series were identified that do not currently have assignments. In total 85 of the 274 lines were identified as belonging to series and 45 have vibronic assignments.

Committee: Frank De Lucia (Advisor); Douglass Schumacher (Committee Member); Thomas Lemberger (Committee Member); Ciriyam Jayaprakash (Committee Member) Subjects: Physics

Master of Science (MS), Wright State University, 2012, Physics

A highly sensitive and selective Terahertz gas sensor used to analyze a complex mixture of Volatile Organic Compounds (VOCs) has been developed. To best demonstrate analytical capabilities of a THz chemical sensor, we chose to perform analytical quantitative analysis of a certified gas mixture using a prototype gas phase chemical sensor that couples a commercial preconcentration system (Entech 7100A) to a custom high resolution THz spectrometer. A Method TO-14A certified mixture of thirty-nine VOCs was purchased. Twenty-six of the thirty-nine chemicals were identified as suitable for THz spectroscopic detection. The Entech 7100A system is designed and marketed as an inlet system for Gas Chromatography Mass Spectrometry (GC-MS) instruments with a specific focus on TO-14A sampling methods and has been incorporated into our spectrometer. Its preconcentration efficiency is high for the thirty-nine chemicals in the mixture used for this study and our preliminary results confirm this for many of the selected VOCs. Presented are the results of this study which will serve as a basis for our ongoing research in environmental sensing and exhaled human breath.

Committee: Ivan Medvedev PhD (Advisor); Doug Petkie PhD (Committee Member); Gary Farlow PhD (Committee Member) Subjects: Physics

PHD, Kent State University, 2011, College of Arts and Sciences / Department of Chemistry

The activity and selectivity of a biologically or pharmacologically relevant molecule are dominated by its molecular shape and conformation. Biomolecular processes in which structure affects function include membrane transport, neurotransmission, drug-receptor interactions, protein-ligand binding, and enzyme catalysis. The overwhelming majority of studies on these molecules are in the condensed phase; solvent effects result in the formation of zwitterions for many of these molecules and thus they lose much conformational freedom. Gas-phase spectroscopy removes solvent and intermolecular interactions resulting in greater conformational freedom and allowing study of neutral species in the isolation required to observe the intrinsic molecular properties of biochemical systems. Fourier-transform microwave (FTMW) spectroscopy, a rotational spectroscopy technique, is a powerful tool for unambiguous structural characterization of gas-phase biomolecules with results directly comparable to theoretical predictions and can be used to characterize the structural preferences of pertinent biomolecules such as dipeptides and biomolecular complexes such as water complexes of biomolecules. The incredible resolution afforded by FTMW spectroscopy allows for the assignment of rotational spectra arising from different conformers, isotopomers, and tautomers. This dissertation describes the rotational spectra and structural characterization of a number of biologically relevant molecules. To increase our capabilities to understand the structures of thermally fragile biological species, we have constructed a laser vaporization sample source for a microwave spectrometer. The design and development of a laser vaporization sample source for microwave spectroscopy is described, and the preparation of samples for a number of species for use in the laser vaporization source and resulting rotational spectra are presented. We utilized FTMW spectroscopy to explore the structures of a number of bio (open full item for complete abstract)

Committee: Michael Tubergen PhD (Committee Chair) Subjects: Chemistry

PHD, Kent State University, 2025, College of Arts and Sciences / Department of Chemistry and Biochemistry

Determining the molecular structure is important to understand the function of a molecule. High-resolution rotational spectroscopy is an invaluable tool to probe the precise 3-dimensional structures of molecules and molecular complexes in gas phase. It can be used to measure a molecule's bond lengths, bond angles, and dihedral angles precisely. The combination of computational chemistry and microwave spectroscopy technique was used to investigate the conformational properties of small biomolecules and molecular complexes. A cavity-based Fourier transform microwave (CB-FTMW) spectrometer was used to record (in the 8-22 GHz frequency range) all the spectra of the molecules and molecular complexes addressed here. In this dissertation, we mainly focused on studying hindered methyl internal rotation (methyl torsion) in small molecular systems. The high resolution of the instrument allows us to record and assign the A- and E- tunneling components along with the nuclear quadrupole hyperfine components that result from the 14N nuclei. The methyl-internal-rotation barrier ranges from 393-411 cm-1 for the series of molecules (valine methyl ester, proline methyl ester, methyl heptanoate, and methyl octanoate) we investigated.

Committee: Michael Tubergen (Advisor); Antal Jákli (Committee Member); Almut Schroeder (Committee Member); Arkaprabha Konar (Committee Member); Hao Shen (Committee Member) Subjects: Chemistry; Physical Chemistry

Doctor of Philosophy (PhD), Ohio University, 2018, Physics and Astronomy (Arts and Sciences)

The question of the immutability of the traditional "magic numbers" and structure of exotic nuclei near to shell closures has long been an area of interest both experimentally and theoretically. The neutron-rich Mg isotopes around N=20 are examples of a region where the expected spherical shell gap has narrowed or disappeared entirely. The "Island of Inversion," centered around 32Mg, is a region where a narrowed N=20 shell gap and collective np-nh excitations result in nuclei with deformed ground states. However, despite years of theoretical and experimental efforts, a complete picture of the detailed nature of deformation in this region has not been achieved and the level schemes remain largely incomplete for many of these neutron-rich nuclei. Furthermore, the presence of rotational band structures, which are key signatures of deformation, have only recently been observed in this region. Two experiments were performed at the National Superconducting Cyclotron Laboratory (NSCL) in order to probe the structure of the A=33 isobars in the "island of inversion." A beta-decay experiment (NSCL e14063) was performed to investigate the level schemes and decay schemes for the decay of 32Na to 32Mg, 33Na to 33Mg, 33Na to 33Mg to 33Al, and 33Mg to 33Al. The details of the experiment are discussed and level schemes and decay schemes, along with the implications for the observed structure. Additionally, the half-lives for 32,33Na and 33Mg were determined. A measurement (NSCL e11029) of the low-lying level structure of 33Mg populated by a two-stage projectile fragmentation reaction and studied with GRETINA was also performed. The experimental setup is discussed along with the gamma-ray singles and gamma-gamma coincidence analysis used to construct the level scheme for 33Mg. The experimental level energies, ground state magnetic moment, intrinsic quadrupole moment, and gamma-ray intensities are compared to a leading order rotational model in the strong-coupling limit. Lastl (open full item for complete abstract)

Committee: Heather Crawford (Advisor); Carl Brune (Committee Member); Daniel Phillips (Committee Member); Alexander Neiman (Committee Member); Katherine Cimatu (Committee Member) Subjects: Nuclear Physics; Physics

Master of Science (MS), Wright State University, 2017, Physics

Terahertz spectroscopy has found use as an analytical tool in determining chemical composition of exhaled human breath. This thesis demonstrates a novel application of this technology - analytical sensing of gaseous metabolic products of several types of human cell cultures. An innovative experimental system was developed for probing cellular metabolism using terahertz [THz] rotational spectroscopy. Gaseous emissions of cell cultures were analyzed and compared between several cell types. Cancerous and healthy lung cells as well as cancerous liver cells were studied. This technique carries a lot of promise as a noninvasive method of distinguishing between cell types and identifying cell pathologies. In this set of experiments, prominent variance in the rates of acetaldehyde metabolism was identified, which can potentially be used as a diagnostic method of cellular identification. Possible applications of this novel technique might extend to the medical field, where it will be used as a non-invasive detection and diagnostic tool.

Committee: Ivan Medvedev Ph.D. (Advisor); Jason Deibel Ph.D. (Committee Member); Jerry Clark Ph.D. (Committee Member) Subjects: Biology; Biomedical Engineering; Biomedical Research; Biophysics; Cellular Biology; Physics

Master of Science (MS), Wright State University, 2014, Physics

Spatially resolved temperature measurements within a microdischarge in atmospheric pressure air have been conducted using Rayleigh scattering of a pulsed ultraviolet laser. Scattering intensity images were used to generate a radial profile of translational temperature, with the analysis based on the ideal gas inverse relationship of temperature and gas density. Rayleigh scattering results were compared to standard optical emission spectral analyses of N2(C3Πu - B3Πg) bands, where the calculated rotational temperatures from emission were in reasonable agreement with the Rayleigh translational temperature profiles.

Committee: Steven Adams Ph.D. (Advisor); Jerry Clark Ph.D. (Committee Chair); Ivan Medvedev Ph.D. (Committee Member) Subjects: Chemistry; Optics; Physics

Doctor of Philosophy (PhD), Wright State University, 2009, Engineering PhD

The use of aerodynamic actuators, such as leading edge slats, trailing edge flaps, roughing strips and ailerons interact with the air during flight, providing maneuverability for air vehicles. These mechanical devices have many inherent, detrimental attributes, such as space requirements on the wing, added wing weight, second response times, increased drag, and increased airframe vibration, resulting in the production of noise. The potential to eliminate or improve upon these detrimental attributes may be realizable by replacing the current mechanical actuators with plasma actuators. Specifically, the surface-discharge-mode, dielectric barrier discharge (SDBD), plasma actuator has a response time on the order of microseconds to milliseconds, does not increase vibration by mounting flush to the wing surface, does not increase drag, and adds negligible weight to the wing. Unfortunately, these devices are not yet powerful enough to perform many of the tasks required for aerodynamic applications; however, they have demonstrated the potential to do so, providing motivation for the current study. Currently, the approach of the research community has focused on coordinating studies designed to determine the physics of the device and parametric studies to determine optimal configurations required for immediate application. In this work, an experimentally based study utilizing optical emission spectroscopy, current-voltage measurements, and a force balance have been successfully applied, contributing new, specific detail to the morphology and characterization of the SDBD. The results of this study were tailored to aid the development of the appropriate, essential physics required for computational modeling of the SDBD. Initially, force measurements of the induced thrust were obtained to demonstrate how week the induced thrust is, justifying the need for a fundamental study. These results are also important in understanding an apparent discrepancy in the reported dependence o (open full item for complete abstract)

Committee: James Menart PhD (Advisor); William Bailey PhD (Committee Member); Jerry Clark PhD (Committee Member); Roger Kimmel PhD (Committee Member); Joseph Shang PhD (Committee Member); Henry Young PhD (Committee Member) Subjects: Electrical Engineering; Fluid Dynamics; Mechanical Engineering; Physics

Doctor of Philosophy, The Ohio State University, 2009, Chemical Physics

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.

Committee: Frank De Lucia PhD (Advisor); James Coe PhD (Committee Member); Linn Van Woerkom PhD (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2002, Physics

This work consists of spectroscopic measurements and analyses of the molecules glycolaldehyde and chlorine nitrate. The glycolaldehyde analysis is of the ground state transitions. Lines were assigned in the 128 to 356 GHz region using data from the FASSST system for a total of 1082 transitions. These were fit with Pickett's spfit programs, using 15 rotational and centrifugal distortion parameters, with an rms of 107 kHz. This analysis can be used to create predictions in the frequency range of the transitions that have been observed in the interstellar medium. The rotational spectra of chlorine nitrate in a large number of vibrational states has been measured and analyzed. For the 35ClONO2 isotopomer, 4 fundamentals and 16 combination bands were analyzed, and for the 37ClONO2 isotopomer, 2 fundamentals and 9 combination bands were analyzed. The data was taken from 122-356 GHZ with the FASSST system, and from 78-118 GHz with a phase-lock synthesizer. Special emphasis was placed on the chlorine nitrate states that had observable vibrational interactions: the 2ν9/ν7 dyad, the 3ν9/ν7ν9 dyad, the 4ν9/ν72ν9/2ν7 triad, the 5ν9/ν73ν9/2ν7ν9 triad, and the ν6ν9/ν5 dyad. The nν9/mν7 family had very similar perturbations, as each interacting pair or trio had the same symmetry and therefore had both anharmonic and c-type coriolis interactions. The ν6ν9 and ν5 states, however, had different symmetry and had only b-type coriolis interactions. All together over 20,000 lines have been assigned for chlorine nitrate. The complete list of states analyzed for 35ClONO2, in order of ascending energy, is: 2ν9, ν7, 3ν9, ν7ν9, ν6, 4ν9, ν72ν9, 2ν7, ν6ν9, ν5, 5ν9, ν73ν9, 2ν 7 ν9, ν62ν9, ν6ν7, 6ν9, ν74ν9, ν4, ν63ν9, and 7ν9. The list for 37ClONO2 cuts off at ν73ν 9. This study is the first extensive demonstration of analyses of previously unknown rotational structures in excited vibrational states. These studies are becoming possible due to the constantly improving sensitivity and spectral (open full item for complete abstract)

Committee: Frank De Lucia (Advisor) Subjects: Physics, Molecular

MS, Kent State University, 2011, College of Arts and Sciences / Department of Chemistry

Microwave spectroscopy is an important tool for gathering information on the structures of molecules. In my research, I have studied the environmentally relevant molecule diethanolamine using microwave spectroscopy. Diethanolamine, a DOT classified environmentally hazardous substance, is commonly used in the production of soaps and other cosmetics. When in the presence of nitrates, diethanolamine is shown to form an extremely potent carcinogen. The study of diethanolamine using microwave spectroscopy provides further information on the molecule, while the rotational transitions recorded can be used in future databases of environmentally hazardous substances. I have obtained the theoretical structures of diethanolamine, along with the rotational spectra of two conformers of the molecule. In addition, the rotational spectra of several isotopomers of diethanolamine have also been found. In addition to studying the environmentally relevant molecule diethanolamine, I have also obtained the rotational spectrum of 2-aminophenol. 2-aminophenol is an interesting molecule to study; with the addition of water, it is unknown if the conformation of 2-aminophenol will change, as other molecules, such as 2-aminoethanol, previously studied have had conformational changes with the addition of water.

Committee: Michael Tubergen (Advisor); Hanbin Mao (Committee Member); Nicola Brasch (Committee Member) Subjects: Chemistry