Studies of atmospheric and interstellar molecules using cavity ringdown spectroscopy

Supersonic jet techniques are used to study molecular species of atmospheric (solvated hydrochloric acid) and interstellar (polycyclic aromatic hydrocarbons, H3+) importance. Absorption spectra of these species were recorded using Infrared Cavity Ringdown Laser Absorption Spectroscopy (IR CRLAS). Basic CRLAS principles are reviewed along with a discussion of the development of the field and the current state of technology. Detailed descriptions of both the pinhole and slit-aperture supersonic jet sources used for the experimental studies are given.; Solvation effects on hydrochloric acid are studied by monitoring spectral shifts in the H-Cl stretching band with increasing solvation. Spectral shifts in the HClH2O cluster from the gas-phase HCl monomer as well as the analogous shift in the D-Cl stretching band in the fully deuterated systems DClD2O and DCl(D2O)2 are determined. Predissociative and infrared vibrational energy redistribution (IVR) lifetime broadening effects among the clusters exhibit the same isotope and cluster size dependence as previously observed in (H2O)n, (D2O) n, and (DF)n systems.; The CH stretching absorption spectra of rotationally cold gas-phase polycyclic aromatic hydrocarbons (PAHs) are studied. Gas-phase spectra were recorded using a heated slit source for naphthalene, anthracene, phenanthrene, pyrene, and perylene. Comparisons with matrix isolation absorption spectra validate the use of Ar matrix spectra for quantitative comparison with gas-phase infrared spectra of PAHs.; IR CRLAS was used to characterize a pinhole direct-current discharge source developed at Berkeley and installed on the ion storage ring CRYRING at the Manne Siegbahn Laboratory in Stockholm, Sweden to make dissociative recombination measurements of H3+ with electrons under interstellar conditions. Results allow comparison with astronomical observations of the diffuse interstellar cloud towards the star zeta-Persei. An enhancement of the cosmic ray ionization rate by a factor of 40, from 3 x 10-17 s-1 to 1.2 x 10-15 s-1 is suggested to account for the interstellar 'over abundance' of H3 +. Additional analysis indicates that H3+ along the zeta-Persei sight line has an anomalous rotational state distribution.; Preliminary results on several projects including laser emission from H2/He, H2O/He, and H2O/Ne supersonic jet DC discharge plasmas; absorption spectra of the intramolecular bending mode of (D2O)2 and of an unidentified species in the HCl/H2O system are also presented.