Rotational relaxation of CO by collisions with H2 molecules: A comparison between theory and experiment

Abstract

A comprehensive study of rotational relaxation of CO(X 1Σ+, v = 1) due to collosions with H2 perturbers is presented. A time-resolved infrared double resonance experiment is described, which yields transfer and decay rates for the rotational levels around j = 10 at liquid nitrogen and room temperatures. Physical conditions of the experiment are discussed in order to justify the approximation used in the analysis. Close coupling calculations, using a previously computed ab-initio potential energy surface, are developed for the CO + H2 (j = 0) collision. The CO + H2 (j = 1) collision rates are limited to low rotational levels, and an extension to high rotational levels using the sudden approximation is presented. Spherical tensor formalism is used to derive cross sections suitable for analysing the polarization effects in the experiment together with the pressure-broadening data. Comparison between theory and experiment shows a reasonable agreement, particularly for the ratios of cross sections, in spite of some discrepancies in the absolute values, which are most noticeable at low temperatures.