TERMOLECULAR RATE COEFFICIENTS AND THE STANDARD ENTHALPY OF THE REACTION OH+CS2+M-]HOCS2+M

The reaction between OH and CS2 has been studied in He in the pressure range 9-270 Torr and the temperature range 249-298 K by means of the laser-photolysis/laser-induced-fluorescence technique. Analysis of the temporal profile of [OH] yielded the rate coefficients for the forward and reverse reactions for the equilibrium OH + CS2 + M reversible HOCS2 + M and hence the equilibrium constant. Study of the temperature dependence of the equilibrium constant leads to the standard enthalpy of reaction DELTA-H-degrees = 43.9 +/- 5.3 kJ mol-1 and the standard entropy of reaction DELTA-S-degrees = 102.9 +/- 15.4 J K-1 mol-1. The termolecular rate coefficients for the forward reaction at 298 K have also been determined to be K(He)(III) = (5.04 +/- 1.01) X 10(-32) cm6 molecule-2 s-1 sand k(CS2)(III) = (4.28 +/- 1.07) X 10(-31) cm6 molecule-2 s-1. The rate coefficients for the reverse reaction at 298 K have been determined to be k(He)(R) = (7.36 +/- 1.47) X 10(-15) cm3 molecule-1 s-1 and k(CS2)(R) = (5.79 +/- 1.45) X 10(-14) cm3 molecule-1 s-1. All uncertainties represent 95% confidence limits. The temperature dependence of k(He)(III) and k(He)(R) corresponds to activation energies E(a) = 13.4 +/- 3.4 and 34.6 +/- 8.7 kJ mol-1, respectively. For the reaction also studied in Ar at 246 K, consistent results have been obtained.