Multiphoton Processes in Gas Mixture: Determination of Rotational Relaxation Parameters

Mira Terzić,^a Dragan D. Markushev,^b  and Mihajlo Rabasović^b

^aFaculty of Science, University of Novi Sad, Trg Dositeja Obradovića 4,  21000 Novi Sad,Serbia and Montenegro.  mterzic@im.ns.ac.yu
^b Institute of Physics, Pregrevica 118, 11080 Beograd-Zemun, Serbia and Montenegro

Abstract
We present a new experimental approach to the study of average macroscopic (bulk) (RgR/T) rotational relaxation parameters of highly vibrationally excited molecules in gas mixtures, where collisions enhance absorption processes. Bulk parameters were derived from measured enhanced cross section, which contains information on photon and collision  physics, by means of calibrated multiphoton photoacoustic spectroscopy. All measurements were carried out at room temperature, for the 10P(16) TEA CO₂ laser line with fluence range of  (1-7)×10³ Jm^-2  and for buffer gas pressures ranging from 1–140 mbar. Particular attention was paid to evaluate the effects of collision partner and buffer pressure dependence on relaxation parameters. Significant buffer pressure effects were observed for all investigated gas mixtures. Two buffer pressure regimes can be distinguished: low and high. It is shown that the data obtained from the proposed method is in good accordance with data obtained from the “slope” and “point” method presented in earlier papers.

Key words: rotational relaxation, multiphoton, photoacoustic spectroscopy