Supersonic molecular beam spectroscopy has great potential for selectivity in chemical analysis. In this work, we used resonant two-photon ionization (R2PI) spectroscopy in supersonic beams in order to obtain ultraviolet ionization spectra with sharp features for unique identification of different species. This wavelength selective ionization was utilized for detection in a time-of-flight mass spectrometer (TOF). The spectroscopy of several disubstituted benzenes have been studied near their origin transitions. These molecules have low quantum yields in fluorescence but can be detected easily with R2PI. Since they absorb at different wavelengths, discrimination of one such compound in a mixture is possible. In aromatic molecules substituted with chlorine and bromine isotopes, relatively large vibrational isotope shifts have been observed (∼2.5 cm\sp{-1}). Isotopic selection was thus observed in the TOF and enhancement factor in the case of chlorine isotopes may be on the order of 60 or more. Substituent effects were studied in the R2PI of mono- and disubstituted halogenated benzenes and halogenated toluene, phenol and aniline derivatives. The ionization phenomena were explained in terms of steric and coulombic interactions, and Frank-Condon transition probability. In the case of azabenzenes, a three-photon process was proposed for the efficient ionization observed. In this process, the first photon excites a molecule to a resonant state, a second photon then excites the molecule to a upper high lying Rydberg state, and a third photon ionizes the molecule. The wavelength spectra reflect the absorption of the n -\ \pi\sp{\*} transition. In order to extend this technique to the analysis of nonvolatile and thermally labile compounds, supercritical fluids were used as the carriers. A pulsed valve has been designed to operate at pressures of up to 380 atm and nearly 200\sp\circC. The reduction in duty cycle has allowed the use of a 200 μm orifice which significantly increases the on-axis density in the jet. Several nonvolatile polynuclear aromatic hydrocarbons have been introduced into the vapor phase and detected using R2PI in the TOF at moderate temperatures. A simple derivatization procedure has been used to increase the solubilities of polar aromatic carboxylic acids for supercritical CO\sb2 and N\sb2O injection into a mass spectrometer. In addition, high pressure liquids such as methanol and water were used to introduce polar aromatic amines into the supersonic beams.Ph.D.Analytical chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/128128/2/8801420.pd
