Pulsed infrared cavity ringdown laser absorption spectroscopy

A high resolution (75 MHz) infrared cavity ringdown (CRLAS) spectrometer employing stimulated Raman scattering (SRS) of a pulsed Alexandrite ring laser as the tunable infrared source has been developed. This spectrometer compliments our medium resolution (1000 MHz) dye laser based infrared cavity ringdown spectrometer. In principle, this spectrometer should provide continuous coverage from 3--8 mum. Current spectral coverage (2200--1710 cm -1) is limited by damage to the Herriot cell mirrors used to facilitate the SRS process. Basic CRLAS principles, SRS principles, and cavity interference effects are reviewed. Applications of this spectrometer to infrared spectroscopy of carbon clusters is discussed, as well as alternative methods for generating infrared light.;The medium resolution CRLAS spectrometer has been used to study hydrogen bonded clusters. A comparative study of small alcohol clusters indicates that the hydrogen bond strength increases as a function of side chain length. The CRLAS results show that several isomers and conformers are present in the molecular beam expansion for a given cluster size except for the methanol dimer which is present in a linear structure. Uracil and thymine clusters, as well as uracil-water complexes have been studied in the NH stretching region. Evidence of extensive clustering in uracil/He and thymine/He expansions is presented. The uracil-water CRLAS data indicate the presence of three isomers of the uracil-water dimer as well as larger complexes. These clusters display extremely strong hydrogen bonds, in agreement with theoretical calculations.