TEMPERATURE AND PRESSURE-DEPENDENCE OF THE MULTICHANNEL RATE COEFFICIENTS FOR THE CH3+OH SYSTEM

Laser flash photolysis measurements on the kinetics of the title syste m in a He bath gas are reported for the temperatures 290, 473, and 700 K and a pressure range of 7.6-678 Torr. CH3 and OH radicals were gene rated simultaneously by 193 nm photolysis of acetone containing traces of water, with CH3 in large excess. The course of reaction was follow ed by monitoring the concentration of OH using laser-induced fluoresce nce (LIF), while CH3 was monitored by absorption at 216.4 nm. The expe rimental data were analyzed in the first instance by a simple model ba sed on the decay of OH and CH3, which was verified by more: comprehens ive numerical simulations. Further analysis of the data, using a combi ned master equation/inverse Laplace transform/RRKM procedure, yielded estimates of the association rate coefficient of CH3 and OH (k(l)(infi nity) = (8.0 +/- 0.3) x 10(-11) (T/300 K-0.79+/-0.09 cm(3) molecule(-1 ) s(-1)) and for the enthalpy change for the CH3 + OH --> (CH2)-C-1 H2O channel (Delta H-0(-) = 1.6 +/- 2.0 kJ mol(-1)). Pressure-dependen t rate coefficients for the various channels are also calculated and p arameters for a modified Troe representation determined.