The microwave spectra and structures of three molecules have been investigated; these are: sulphur dichloride (SCI₂), dichlorosilane (SiH₂Cl₂) and propiolyl chloride (H-C=C-C0Cl). Sulphur Dichloride: The microwave spectra of ³²S³⁵Cl₂ in the ground and v₂ = 1 excited vibrational states, and of ³²S³⁵Cl³⁷Cl in the ground state have been measured in the 12-40 GHz frequency region. The spectra of the ground state species have been analysed to yield values for the rotational constants, the quartic centrifugal distortion constants and a partial set of sextic centrifugal distortion constants. Precise rotational constants have been obtained for the v₂=1 excited state of ³²S³⁵Cl₂. A complete set of harmonic force constants has been determined from the quartic centrifugal distortion constants and the variation of the inertial defect with vibrational state. The wavenumbers of the three vibrational fundamentals of sulphur dichloride have been predicted, and are in excellent agreement with the observed values. An effective and a partial substitution structure for sulphur dichloride have been evaluated from the ground state rotational constants. The harmonic force constants have been used to obtain the average structures of ³²S³⁵Cl₂ in the ground and v₂=1 states. The ground state average structural parameters of 32S35C12 are: r[sub=z](S-Cl) = 2.01525 ± 0.00008 Å and <(Cl-S-Cl) = 102.730 + 0.005° The equilibrium structure of sulphur dichloride has also been estimated. Dichlorosilane: The microwave spectra of ²⁸SiH₂³⁵Cl₂, ²⁸SiH₂³⁵Cl³⁷Cl and ²⁹SiH₂³⁵Cl₂ have been measured in the 8-40 GHz frequency range. The spectra have been analysed to yield values for the rotational constants, quartic centrifugal distortion constants and chlorine nuclear quadrupole coupling constants, as well as the molecular dipole moment, 1.129 ± 0.020 Debye. The molecule has been shown to have C₂v symmetry. Effective and partial substitution structures have been obtained for dichlorosilane using the experimental values for the rotational constants. Further, the quartic centrifugal distortion constants have been combined with existing vibrational data to determine a harmonic force field which, in turn, has been used to derive the ground state average structural parameters of ³²S³⁵Cl₂.These are: r[sub=z] (Si-Cl)=2.0352 ± 0.0003 Å, <(C1-Si-Cl) = 109.68 ± 0.03°; r[sub=z](Si-H)=1.4726 ± 0.0025 Å , <(H-Si-H) =112.44 ± 0.28°. The equilibrium structure of dichlorosilane has also been estimated. Propiolyl Chloride: The microwave spectra of HCCCO³⁵Cl, HCCCO³⁷C1, DCCCO³⁵Cl.and DCCCO³⁷CI have been measured in the ground and, except 37 for DCCCO³⁷CI, the vg = 1 vibrational states. The spectra have yielded values for the rotational constants, quartic centrifugal distortion constants and chlorine nuclear quadrupole coupling constants, as well as the molecular dipole moment, 2.717 ± 0.035 Debye. The quartic centrifugal distortion constants have been combined with existing vibrational data to determine an approximate harmonic force field. Having assumed a reasonable structure for the ethynyl group, the force field was used to obtain the ground state average structure of propiolyl chloride. These results suggest that the carbon chain in propiolyl chloride has a deviation from linearity of less than one degree. / Science, Faculty of / Chemistry, Department of / Graduate

Tunable high order anti-Stokes radiation produced by stimulated Raman scattering in liquid nitrogen is studied experimentally. The light beams of two lasers of different frequencies a ruby laser and tunable dye laser --.are simultaneously focussed in liquid nitrogen and two distinct series of anti-Stokes lines are observed. The dye laser anti-Stokes lines can be changed in frequency by tuning the dye laser. The intensities of the two series of lines are investigated as a function of both ruby and dye laser power, The dye laser anti-Stokes line intensities are found to have a distinct threshold for ruby laser power but no threshold for dye laser power. The experimental results support a two step model in which the ruby laser acts as a pump for molecular vibrations which in turn modulate the dye laser frequency. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The E2 cross section for the ¹²C(p,Ύ₀)¹³N reaction has been measured from 10 MeV to 17 MeV in the laboratory system by bombarding an enriched carbon-12 target with beams of polarized protons. A 10 in. φ x 10 in, Nal(Tl) detector with a plastic anti-coincidence shield was used to detect the gamma rays. The total E2 capture cross sections were of the order of 0.2 ybarns and no resonance effects were observed. The amount of the E2 energy-weighted sum rule depleted in this energy range is (10.3 ± 4.0)%. Calculations based on a direct semi-direct capture model provide a good description of the experimental results by including only direct E2 capture and direct plus collective E1 capture. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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No description available.

The vacuum ultraviolet molecular hydrogen laser is evaluated as a selective ion source for analytical mass spectrometry of easily-ionized compounds. The types of compounds ionized below the photon energy of 7.8 eV include polynuclear aromatic hydrocarbons, and many amines and nitrogen-containing heterocycles. The latter two categories encompass a large number of pharmaceuticals and drugs of abuse. H₂ laser photoionization produces parent molecular ions only, for all compounds studied thus far. Selectivity of the threshold photoionization process is very high, as compounds within as little as 0.2 eV above the threshold are completely rejected. The ability of the technique to discriminate against interfering matrix components is demonstrated for both simple synthetic and complex "real world" mixtures. Easily interpreted spectra are obtained from simple extracts of spiked coffee, beer, soy sauce, urine and blood serum. The most important interference is shown to be electron impact ionization arising from acceleration of stray electrons in the ion source. Most of this ionization is caused by low-energy secondaries generated when stray primaries are collected by the ion source electrodes. The primaries are produced mainly by interaction of scattered laser radiation with metal surfaces. This interference can be controlled through proper instrumental design.

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Many materials such as drugs and explosives have characteristic spectral signatures in the terahertz (THz) band. These unique signatures imply great promise for spectral detection and classification using THz radiation. While such spectral features are most easily observed in transmission, real-life imaging systems will need to identify materials of interest from reflection measurements, often in non-ideal geometries. One important, yet commonly overlooked source of signal corruption is the etalon effect - interference phenomena caused by multiple reflections from dielectric layers of packaging and clothing likely to be concealing materials of interest in real-life scenarios. This thesis focuses on the development and implementation of a model-based material parameter estimation technique, primarily for use in reflection spectroscopy, that takes the influence of the etalon effect into account. The technique is adapted from techniques developed for transmission spectroscopy of thin samples and is demonstrated using measured data taken at the Northwest Electromagnetic Research Laboratory (NEAR-Lab) at Portland State University. Further tests are conducted, demonstrating the technique's robustness against measurement noise and common sources of error.