M.W.P. Strandberg, T. Wentink, Jr. [and] R.L. Kyhl. / "May 13, 1948." / Bibliography: p. 17. / Army Signal Corps Contract W-36-039 sc-32037.

High-resolution pulsed beam Fourier Transform Microwave Spectroscopy (PBFTMS) technique has been used to investigate the rotational spectra, molecular structures and electronic charge distribution of organometallic and organic molecules. The thesis reports high-resolution rotational spectral findings for nine different asymmetric-top molecules in the singlet electronic ground state including: Cyclopentadienyltungstentricarbonylhydride, Bis-(cyclopentadienyl)tungstendihydride, Tetracarbonylethyleneosmium, two substituted Ferrocenes and an organic keto-enol tautomeric system, Z-2-Hydroxypyridine and 2-Pyridone. Moreover, gas-phase rotational constants and distortion constants have also been reported for an excited vibrational state of Cyclopentadienylnickelnitrosyl complex using a high-resolution Fourier Transform Spectrometer (FTS) system at Kitt Peak Arizona, (KPNO). Preliminary microwave results for a fluxional molecule, Cyclopentadienyliridiumdicarbonyl are also presented in this work. Extensive Density Functional Theory (DFT) calculations have been performed in conjunction with the experiments to provide additional insight toward further understanding the equilibrium structures, structural isomers and electric field distributions of these molecules. These calculations were not only helpful in predicting the preliminary structure and rotational constants of the molecules of interest, but also advantageous in analyzing the observed spectra.

Thesis (M.S.)--University of Michigan, 1990.

The investigation of the rotational spectra of fluoroformyliminosulfur difluoride, SF2NCOF, and pentafluorosulfanyliminosulfur difluoride, SF2NSF5 , was undertaken to determine, from the experimental moments Q.f inertia, the number and type of positional isomers and the bonding parameters. SF2NCOF and SF2NSF5 are the first iminosulfur difluorides (RN=SF2) to be investigated by microwave spectroscopy. The iminosulfur difluorides are characterized by a nitrogen-sulfur double bond with nonbonding pairs of electrons in an sp2 hybridized orbital on the nitrogen atom and in an sp3 hybridized orbital on the sulfur atom. This bonding scheme is expected to impart a unique charge distribution in the vicinity of the SF2 fluorines. In SF2NCOF the nitrogen-carbon bond may acquire some partial double bond character which can be described through resonance involving the S, N, C, and 0 atoms. The extent of this resonance would be expected to affect the length of the NC bond and to influence the height of the barrier to rotation about this bond. For SF2NCOF and SF2NSF51 the question of cis-trans conformation about the nitrogen-sulfur double bond will be considered. Additionally, several rotameric forms of SF2NCOF which can arise from rotation about the nitrogen-carbon axis and which cannot be definitely precluded by presumptive reasoning will also be examined. / Ph. D.

The rotational spectra of the 2-cyano-2-propyl and d⁶-2·cyano-2-propyl radicals were observed using a Stark modulated spectrometer. The radicals were generated in the gas phase by UV irradiation of sublimed azoisobisbutyronitrile. They were detectable in the cell for approximately one hour. Thirty-three transitions were assigned for (CH₃)₂CCN and twenty-one for (CD₃)₂CCN. The rigid rotor rotational constants determined by calculation of the hypothetical unsplit rotational transitions are A=8276.7, B=3919.7, C=2751.5Mhz for (CH₃)₂CCN and A=6241.3, B=3490.7, C=2372.6Mhz for (CD₃)₂CCN. A program to calculate the fine splittings and hyperfine splittings due to the ¹⁴N nucleus and six protons was written. The spin rotation constants determined for the two species were E_aa=-69.9, E_bb=-36.1, E_cc=2.7Mhz and E_aa=-55.4, E_bb=-32.6 Mhz for (CH₃)₂CCN and (CD₃)₂CCN respectively. The hyperfine coupling constants for ¹⁴N are identical for both isotopic species and were found to be T_aa=-17.2, T_bb=-17.1 and T_cc=34.4 Mhz. The proton and deuteron hyperfine splittings were not resolved. The structural parameters determined from an <r₀> fit of the moments are r_CN=1.18A, r_CC=1.42A, r_CMe=1.50A and CCMe=119.3°. The C₄N skeletal framework was found to be planar. / Ph. D.

A resonant microwave cavity technique was employed to study the dielectric behavior of some polar and non-polar liquids near the phase transition temperatures at microwave frequencies of 7.2, 9.2 and 10.1 GHz. The Slater perturbation equations for a resonant microwave cavity are briefly discussed to show that the above technique can be used to determine both the real and imaginary parts of dielectric response. Abrupt changes in dielectric response were observed near the phase transition temperatures for the polar liquids studied in this investigation. The dielectric relaxation phenomenon in liquids has been treated as a chemical rate process and the abrupt change in the dielectric response of the liquids near phase transition temperatures is shown to be related to the dramatic changes in the free energy of activation of the molecules. Some values of the free energy of activation were deduced for the various compounds from data obtained in this investigation.

A double modulation microwave spectrometer is used to evaluate the linewidth parameters for some excited rotational components in the bending vibration v_8 of 13CH3 13C 15N and 13CH3C15N isotopomers of methyl cyanide. The linewidth parameters for self-broadening of the ΔJ=2←1 rotational components for the ground v_8 , 1v_8, and the 2v_8 vibrations were determined over a pressure range of 1 to 13 mtorr and at a temperature of 300 K. The double modulation technique is used to explore the high eighth derivative of the line shape profile of the spectral line. This technique proved to give good signal-to-noise ratios and enabled the recovery of weak signals. An experimental method is developed to correct for source modulation broadening. The tests of the ratios of the two inner peak's separation of the eighth derivative of the line showed that they were up to 95% similar to those for a Lorentzian line shape function. The line shapes were assumed to be Lorentzian for the theoretical analysis of the derivative profiles and comparisons were made between experiment and theory on this basis. Dipole moments for vibrationally excited states were calculated from linewidth parameters and show systematic decrease with the increase of excitation. Impact parameters were calculated using the "hard sphere" model of the kinetic theory of gases. The results were many times larger than the size of the molecule itself. This suggests that the dominant interaction is a long range dipole-dipole force interaction.

A source-modulation microwave spectrograph was utilized to measure line width parameters for several spectral lines in the pure rotational spectrum of formaldehyde (H₂CO). The spectrograph featured high-gain ac amplification and phase-sensitive detection, and was capable of measuring microwave lines having absorption coefficients as small as 10⁻⁷ cm⁻¹ with a frequency resolution on the order of 30 kHz. Center frequencies of the measured lines varied from 4,830 MHz to 72,838 MHz; hence, most of the observations were made on transitions between K-doublets in the rotational spectrum. Corrections were applied to the measured line width parameters to account for Doppler broadening and, where possible, for deviations due to magnetic hyperfine structure in some of the K-doubled lines. Low modulation voltages and low microwave power levels were used to minimize modulation and saturation broadenings; other extraneous broadenings were found to be insignificant. The primary broadening mechanism at low gas pressure is pressure broadening, and a review of this topic is included. Line width parameters for the several observed transitions were determined by graphing half-widths versus pressure for each spectral line, and performing a linear least-squares fit to the data points. Repeatability measurements indicated the accuracy of the line width parameters to be better than ±10 percent. The reasons for this repeatability spread are discussed, Broadening of each line was measured for self- and foreign-gas broadening by atomic helium and diatomic hydrogen. Effective collision diameters were calculated for each broadening interaction, based on the observed rates of broadening.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Stanley Richard Rotman. / B.S.

Pulsed terahertz (THz) systems are an emergent technology, finding diverse applications as they approach maturity. From their birth in the late 1980's to the wealth of alternate sources and imaging modalities now available, the rise has been fuelled by the expectation that this will prove a world changing technology. This Thesis takes an application focused approach and seeks to provide enabling systems and algorithms for the development of functional imaging systems with broad potential application in security inspection, non-destructive testing and biomedical imaging. Three dimensional pulsed THz imaging systems were first introduced in 1996 using a reflection-mode ultrasound-like configuration. This Thesis builds upon this former work by focusing on transmission mode tomography systems using pulsed THz radiation. Several novel 3D imaging modalities are introduced. The hardware architectures, based on optoelectronic generation and detection of THz radiation are described. Approximations to the wave equation are derived, allowing linear reconstruction algorithms to recover 3D structural information fromthe transmitted THz field. Finally the systems are demonstrated and the achievable resolution and image quality are investigated. Three imaging architectures are developed herein: 1. T-ray holography allows the 3D distribution of point scatters to be resolved based on a single projection image utilising a novel reconstruction algorithm based on the windowed Fourier transform and back-propagation of the Fresnel-Kirchhoff diffraction equation. 2. T-ray diffraction tomography utilises the diffracted THz field to allow a Helmholtz equation based, frequency-dependent reconstruction to be performed and the THz spectrum at each pixel to be calculated. 3. T-ray Computed Tomography (CT) uses analogous techniques to X-ray CT, based on the Radon transform, to provide 3D T-ray reconstructions of unprecedented fidelity. These techniques have important applications in material identification, which is investigated in the second part of this Thesis. Pulsed THz spectroscopy has been widely acclaimed for its potential to identify different materials based on their spectral properties. The second part of this Thesis presents algorithms towards this goal. Three case studies are performed focusing on biomaterial classification, anthrax detection and in vitro osteosarcoma cell differentiation. A classification framework is developed to process the THz spectral data and identify specific materials. A linear filter model is introduced to describe the system response of different materials, and the filter taps are utilised for feature extraction. This technique is demonstrated for biomaterial and anthrax classification. For cell differentiation a genetic algorithm is used to select deconvolved frequency components to train a classifier. In each case a high classification accuracy is demonstrated, highlighting the promise and potential of three dimensional T-ray inspection systems. / Thesis (Ph.D.)--School of Electrical and Electronic Engineering, 2004.