Measurement of rotational relaxation in the ground state of methane perturbed by argon at low temperature

Relaxation processes at low temperature in methane perturbed by argon have been investigated on the basis of new measurements. Diode laser absorption spectra of methane in the region of the dyad v(2)/v(4) in supersonic expans ions have been recorded. The time of relaxation of the ground state mean ro tational energy was derived from the observed dependences of the rotational temperature on the concentration in the jet. A semi-classical model was us ed to calculate the state-to-state relaxation rate constants at room temper ature. The evaluation of the time of relaxation of the mean rotational ener gy using semi-empirical temperature dependence laws is presented and discus sed. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.