Typescript. Includes vita and abstract. Includes bibliographical references (leaves 273-280) Also available online in Scholars' Bank; and in ProQuest, free to University of Oregon users.

The response of a polyatomic gas to microwave radiation including both steady state (pressure broadening) and time dependent (coherence transients) effects - is described theoretically. The treatment is based on solutions of a quantum mechanical Boltzmahn equation and employs kinetic theory methods which have previously been used in the explanation of the field dependence of transport phenomena (Senftleben-Beenakker effects). Much of the recent theoretical work of pressure broadening and coherence transient phenomena is based on a two (energy) state model for the gas molecules. This model, when developed from a density operator point of view, results in a coupled set of three equations which are mathematically equivalent to the Bloch equations of NMR. The present work reexamines this description, and replaces it with a two level model for the gas system. Here, the term "level" implies explicit consideration of the rotational (magnetic) degeneracy associated with each energy state. This model gives a more appropriate representation of the interaction of microwave radiation with a real molecular system. In particular, a more complete set of coupled equations result from this description and involve quantities in addition to the three moments used in a two state approach. The most important of these latter effects are represented by spherical harmonics Ƴ(q) (J) in he angular momentum J of the relevant energy levels. An analogous treatment of rotational effects has previously been used in Senftleben-Beenakker studies. Specific molecular types of interest in microwave spectroscopy -diamagnetic diatonics and linear polyatomics, symmetric tops, and inverting symmetric tops - are treated separately by this two level approach. The vector (and tensor) nature of the motions are emphasized throughout. The number of rotational polarizations that arise in the general two level case is often quite large. The simplest example of a two level system is the j=0 to j=l transition of a diamagnetic diatomic. This is studied in some detail. Here, the scalar component Ƴ⁽²⁾⁰(J) is the only rotational polarization affected by linearly polarized radiation in the usual experiments. The effect of this quantity on both steady state and transient phenomena is described, and a new "combination" experiment is suggested as the best way to detect the presence of this additional polarization. The Doppler effect is treated by appropriately including the effects of translational motion in the quantum Boltzmann equation. A more general set of coupled moment equations then results, and the manner in which the macroscopic velocity polarizations arise is thereby established. A model method solution of the quantum Boltzmann equation, emphasizing the parity invariance of the collision super-operator, is given for a steady state absorption experiment in the absence of saturation but including Doppler effects. Throughout this thesis, the relaxation rates, are related to kinetic theory collision cross sections by solving the quantum Boltzmann equation. Extensive use is made of rotational invariance to reduce the number of independent collision integrals, and their approximate evaluation is accomplished within the context of the distorted wave Born approximation. All collision integrals for the pure internal state polarizations are found to-be expressible in terms of one translational factor, which is itself further approximated by a modified Born approximation. Correspondingly, the translational factor which arises in the relaxation of macroscopic velocity polarizations is completely specified by relating it to the Ω(ℓ,s) integrals of traditional kinetic theory. / Science, Faculty of / Chemistry, Department of / Graduate

No description available.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 1976 / Vita. / Includes bibliographical references. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Chemistry

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xiv, 218 p.; also includes graphics (some col.) Includes bibliographical references (p. 208-218). Available online via OhioLINK's ETD Center

No description available.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 1975 / Vita. / Includes bibliographical references. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Physics

xvi, 280 p. : ill. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / Doppler-limited, steady-state, linear absorption spectra of 127 I 2 (diatomic iodine) near 675 nm were recorded with an internally-referenced wavelength modulation spectrometer, built around a free-running diode laser using phase-sensitive detection, and capable of exceeding the signal-to-noise limit imposed by the 12-bit data acquisition system. Observed I 2 lines were accounted for by published spectroscopic constants. Pressure broadening and pressure shift coefficients were determined respectively from the line-widths and line-center shifts as a function of buffer gas pressure, which were determined from nonlinear regression analysis of observed line shapes against a Gaussian-Lorentzian convolution line shape model. This model included a linear superposition of the I 2 hyperfine structure based on changes in the nuclear electric quadrupole coupling constant. Room temperature (292 K) values of these coefficients were determined for six unblended I 2 lines in the region 14,817.95 to 14,819.45 cm -1 for each of the following buffer gases: the atoms He, Ne, Ar, Kr, and Xe; and the molecules H 2 , D 2 , N 2 , CO 2 , N 2 O, air, and H 2 O. These coefficients were also determined at one additional temperature (388 K) for He and CO 2 , and at two additional temperatures (348 and 388 K) for Ar. Elastic collision cross-sections were determined for all pressure broadening coefficients in this region. Room temperature values of these coefficients were also determined for several low- J I 2 lines in the region 14,946.17 to 14,850.29 cm -1 for Ar. A line shape model, obtained from a first-order perturbation solution of the time-dependent Schrödinger equation for randomly occurring interactions between a two-level system and a buffer gas treated as step-function potentials, reveals a relationship between the ratio of pressure broadening to pressure shift coefficients and a change in the wave function phase-factor, interpreted as reflecting the "cause and effect" of state-changing events in the microscopic domain. Collision cross-sections determined from this model are interpreted as reflecting the inelastic nature of collision-induced state-changing events. A steady-state kinetic model for the two-level system compatible with the Beer-Lambert law reveals thermodynamic constraints on the ensemble-average state-changing rates and collision cross-sections, and leads to the proposal of a relationship between observed asymmetric line shapes and irreversibility in the microscopic domain. / Committee in charge: David Herrick, Chairperson, Chemistry; John Hardwick, Advisor, Chemistry; Jeffrey Cina, Member, Chemistry; David Tyler, Member, Chemistry; Michael Raymer, Outside Member, Physics

abstract: One strategic objective of the National Aeronautics and Space Administration (NASA) is to find life on distant worlds. Current and future missions either space telescopes or Earth-based observatories are frequently used to collect information through the detection of photons from exoplanet atmospheres. The primary challenge is to fully understand the nature of these exo-atmospheres. To this end, atmospheric modeling and sophisticated data analysis techniques are playing a key role in understanding the emission and transmission spectra of exoplanet atmospheres. Of critical importance to the interpretation of such data are the opacities (or absorption cross-sections) of key molecules and atoms. During my Doctor of Philosophy years, the central focus of my projects was assessing and leveraging these opacity data. I executed this task with three separate projects: 1) laboratory spectroscopic measurement of the infrared spectra of CH4 in H2 perturbing gas in order to extract pressure-broadening and pressure-shifts that are required to accurately model the chemical composition of exoplanet atmospheres; 2) computing the H2O opacity data using ab initio line list for pressure and temperature ranges of 10^-6–300 bar and 400–1500 K, and then utilizing these H2O data in radiative transfer models to generate transmission and emission exoplanetary spectra; and 3) assessing the impact of line positions in different H2O opacities on the interpretation of ground-based observational exoplanetary data through the cross-correlation technique. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2019

Analyzing stellar spectra plays a big role in understanding the evolution of our galaxy. Having good data for spectral line properties is very important when analyzing these spectra. One part of the Gaia-ESO public spectroscopic survey (GES) is to gather data for spectral line properties from stellar spectra. The scope of this project is to study one of these properties, the spectral line width caused by collisional broadening by hydrogen. Collisional broadening by hydrogen occurs when a hydrogen atom collides with a particle. The goal of this project is to successfully calculate the collisional spectral line broadening of iron lines where new data is missing from the GES using modern quantum mechanical calculations. These calculations are done using the ABO theory, which is more advanced than previously established theory.A table of Fe-I (Neutral iron) spectral lines without collisional broadening data in the GES has been provided. Using the ABO theory and the accompanying ABO cross section calculator code, estimates of collisional broadening by hydrogen have been calculated for these lines. The new calculations predict that the line width of the spectral lines are typically twice as large compared to older estimates calculated using simpler theory. This new data can be expected to improve stellar spectrum analysis in the Gaia-ESO survey spectra. / Analys av stjärnspektran spelar en stor roll i vår förståelse av vintergatans utveckling. Att ha bra data för spektrallinjers egenskaper är oerhört viktigt vid analys av dessa spektran. En del i Gaia-ESO public spectroscopic survey (GES) är att samla in data för dessa spektrallinjers egenskaper ur stjärnspektran. Omfattningen av detta projekt innefattar att titta närmare på en av dessa egenskaper, spektrallinjebreddning orsakad av kollisionsbreddning av väte. Kollisionsbreddning av väte uppstår när en väteatom kolliderar med en annan partikel. Målet med projektet är att med framgång beräkna kollisionsbreddningen av spektrallinjer från järn där ny data saknas ur GES genom att använda moderna kvantmekaniska beräkningar. Dessa beräkningar är gjorda med den så kallade ABO-teorin, vilken är mer avancerad än tidigare etablerade teorier. En tabell med Fe-I (neutralt järn) spektrallinjer utan kollisionsbreddningsdata i GES har tillhandahållits. Med hjälp av ABO-teorin och den medföljande ABO-tvärsnittsräknar-koden har beräkningar av kollisionsbreddning med väte utförts för dessa linjer. De nya beräkningarna förutser att spektrallinjernas bredd blir typiskt två gånger så stor jämfört med de äldre beräkningarna gjorda med enklare teori. Denna nya data kan förväntas att förbättra analysen av stjärnspektrum ur Gaia-ESO kartläggningen.