R. Casaes

Infrared cavity ringdown spectroscopy of methanol clusters: Single donor hydrogen bonding

Infrared cavity ringdown laser absorption spectroscopy has been used to study the O–H stretching vibrations of jet-cooled methanol clusters in direct absorption. Rovibrational bands for (CH3OH)2, (CH3OH)3, and (CH3OH)4 have been measured. Both bonded and free O–H stretches were measured for the dimer, indicating that its structure is linear. Five bands were assigned to the methanol trimer, indicating the presence of a second cyclic isomer in the molecular beam. A detailed study of the free O–H stretching region shows that methanol clusters larger than dimer must exist in cyclic ring configurations. In order to facilitate spectral assignment, harmonic frequencies and infrared intensities were calculated for the methanol monomer, dimer, and trimer with second order Mo/ller–Plesset perturbation theory. Using the theoretical infrared intensities and measured vibrational band absorptions, absolute cluster concentrations were calculated. Results agree with previous experimental and theoretical work.

A re-examination of the 4051 Å band of C3 using cavity ringdown spectroscopy of a supersonic plasma

The C3 molecule is of fundamental interest to chemists, both as the simplest cumulene and as a prototypical nonrigid system.It is also of great importance in astrophysics, as it now serves as a remote diagnostic of the temperature and density of interstellar clouds.However, high resolution astronomical spectra have uncovered a discrepancy between the observed R(0) transition and the laboratory spectrum.We have used cavity ringdown spectroscopy to obtain a high resolution, low temperature spectrum of the 4051 A band, and have confirmed that the R(0) transition was incorrectly assigned in previous laboratory work. 2003 Elsevier Science B.V. All rights reserved.

High resolution pulsed infrared cavity ringdown spectroscopy: Application to laser ablated carbon clusters

We report the design and performance of a tunable, pulsed high resolution mid infrared cavity ringdown spectrometer. Stimulated Raman scattering in H2/D2 is used to downconvert the output of a SLM Alexandrite ring laser (720–800 nm) to the mid infrared (3–8 μm). The infrared frequency bandwidth was determined to be 90±5 MHz from measurements of Doppler broadened OCS transitions at 5 μm. The minimum detectable per pass fractional absorption is 1 ppm. We observe a frequency dependent ringdown cavity transmission of ±5 ppm due to spatial variations of the mirror reflectivity. The υ6 band of linear C9 formed by laser ablation of graphite in a He molecular beam was measured, showing a factor of 2 improvement in sensitivity relative to previous IR diode laser experiments. Based on calculated IR intensities, the number density of C9 in the molecular beam is 1.3*1011 molec/cm3 and the minimum detectable density is 1*109 molec/cm3. We expect this spectrometer to be a powerful tool for the study of transient specie...