Matrix isolation resonance Raman and cavity ringdown spectroscopy of species of astrophysical interest

Carbon clusters and ionized polycyclic aromatic hydrocarbons have generated much interest in the fields of astrophysics and physical chemistry. It has been hypothesized that these species are responsible for the diffuse interstellar bands (DIBs). Two projects are the focus of this dissertation. The first is resonance Raman spectroscopy of matrix-isolated linear carbon clusters, and the second project is construction and operation of a cavity ringdown spectrometer.; In the first project, odd-numbered linear carbon clusters were produced by laser ablation of graphite and were trapped in solid Ar at 12 K. These clusters were then probed using resonance Raman spectroscopy. This was done to confirm previous empirical assignments of the 1Σ _u-1Σ_g electronic transitions of the respective clusters. The most intense Raman feature in all clusters was the lowest energy totally symmetric, σ_g, carbon-carbon stretch. Observed Raman frequencies were compared with density functional theory calculations at the B3LYP/6-311G* level of theory.; Cavity Ringdown Spectroscopy (CRDS), the focus of the second project, is a relatively new, high sensitivity direct absorption technique based on light trapped between two high reflectivity mirrors. A CRDS instrument was constructed and tested to determine its effectiveness in measuring electronic spectra of transient species. The testing phase involved measuring the doubly forbidden 1Σ_u-3Σ _g transition in oxygen and the S₁-S₀ transition of jet-cooled azulene. Finally the D₂-D₀ transition of the naphthalene cation, produced in a pulsed supersonic discharge, was measured, revealing two broad bands at 648.8 and 670.4 nm, which were compared to the DIBs.