Instrumental Advances and Applications in Millimeter/Submillimeter-Wave Spectroscopy

Abstract

Novel applications of Gaussian beam optics were developed and employed in this work toward a new design for the 2nd generation high-temperature direct-absorption spectrometer in the Ziurys laboratory, making a 3rd generation spectrometer. The first instance of an offset-ellipsoidal reflector in a laboratory rotational spectrometer has been employed in combination with a new Gaussian-beam optics design the author of this thesis calls a pseudo-frequency-independent Gaussian beam telescope, or “fiGBT.” This optical arrangement allows for a system that behaves like a Gaussian beam telescope, yet employs an offset ellipsoidal reflector, of which a traditional GBT cannot. Effectively, only one adjustment is needed in the optical system. The location of the adjustment has been chosen to occur conveniently at the source stage, and its magnitude over the 160 GHz to 1 THz operating frequency range of the instrument has been minimized to less than 5 cm. Moreover, the design eliminates the need for specific lenses for various frequency ranges, using only one static feed horn lens for the entire frequency range. The 3rd generation and 1st generation spectrometers, in addition to the Fourier-transform millimeter-wave spectrometer, were applied toward the high-resolution spectroscopic studies of F2SO and the YOH/YOD systems, respectively. F2SO data were analyzed with a Watson A-reduced asymmetric-top Hamiltonian in a combined-fit with previous microwave measurements, and highly accurate rotational and centrifugal distortion constants were determined, including sextic distortion terms that were previously undefined. These parameters are the most accurate set of spectroscopic constants to date for F2SO. Bond angles and bond lengths, in addition to spectroscopic constants, were determined for both systems and reported in the literature. Steps toward magnetic confinement of ions in the velocity modulation spectrometer were taken, and the knowledge gleaned was used to suggest a possible method to increase ion signals in the direct absorption spectrometers having Broida-type ovens.