Rate Constants for the Relaxation of CH(X2Π,ν=1) by CO and N2 at Temperatures from 23 to 584 K

Abstract

Rate constants have been determined for the collisional relaxation of CH(X2Π,ν=1) by CO and N2 over a wide range of temperatures. Experiments between 584 and 86 K have been performed in heated and cryogenically cooled cells, and rate constants from 295 to 23 K have been measured in a CRESU (cinetique de reaction en ecoulement supersonique uniforme) apparatus. In both series of experiments, pulsed laser photolysis was employed to generate CH radicals and the laser-induced fluorescence technique was used to observe the rate of removal of CH(ν=1). Vibrational relaxation is rapid, k298 = 9.7 × 10-11 cm3 molecule-1 s-1 for CO and k298 = 3.1 × 10-11 cm3 molecule-1 s-1 for N2, and the dependence of the rate constants on temperature is quite slight but complex. The results suggest that relaxation occurs via strongly bound complexes, and the implications of the results for the interpretation of the reactions between CH radicals and CO and N2 are discussed.