ENERGY-TRANSFER REACTIONS OF THE HE(3 S-2) ATOM WITH METHANE AND CHLOROMETHANE MOLECULES UNDER BEAM CONDITIONS

Energy transfer reactions of metastable He(2 3S) with methane and chlo romethane molecules were investigated by measuring the emission spectr a of the electronically excited fragments under beam conditions. The f ormation rate constants of the fragments CH(A 2DELTA), CH(B 2SIGMA-), CH (C 2SIGMA+), H and CCl(A 2DELTA) for the reactions He(2 3S) + CHNC l4-n (n=1-4) have been determined. The nascent rovibrational distribut ions of CH(A 2DELTA, upsilon'=0-2) and CH(B 2SIGMA-, upsilon'=0) have been obtained. The experimental results show that the rotational distr ibution of CH(A 2DELTA, upsilon'=0) from the reaction of He (2 3S) wit h methane is different from that of He(2 3S) with chloromethanes. In t he former case, the rotational distribution can be expressed by a sing le Boltzmann temperature, while in the latter it is not a complete equ ilibrium distribution and may be expressed by a double Boltzmann distr ibution. A discussion of the reaction mechanism based on statistical t heory is presented.