Vibrational energy transfer in carbon monoxide at low temperatures

Abstract

The relaxation of vibrationally excited CO has been studied by a gain/absorption technique. Radiation from a stabilised, single frequency cw CO laser is passed through a cell containing a mixture of CO and He which is excited by a pulsed electric discharge. The subsequent gain and/or absorption is measured as a function of time. Data have been obtained on bands from (5, 4) to (11, 10) with the cell walls at 77 and 195 K. The lower levels relax preferentially, resulting in complete population inversions, and rate constants have been extracted for the processes: CO(v)+ CO(v= 0)→ CO(v–1)+ CO(v= 1)–ΔE, with 4 ⩽v⩽ 10. The comparatively mild dependence of the rate coefficients on temperature and ΔE is consistent with energy being transferred under the influence of attractive intermolecular forces. The importance of collisions between excited molecules in our system, and in practical lasers, has been assessed in computer calculations.