A temperature dependence kinetic study of O((1)D)+CH(4): overall rate coefficient and product yields

Using a recently-developed chemiluminescence technique for monitoring O((1)D), the rate coefficient, k(1), of the important atmospheric reaction O((1)D) + CH(4) -> products has been determined over a wide temperature range, 227 to 450 K. The rate coefficient was shown to be independent of temperature, having a value of (1.91 +/- 0.08) x 10(-10) cm(3) s(-1); the quoted uncertainties are with 95% confidence. This highly precise value, based on an extended set of determinations with very low scatter, is significantly greater, 26%, than current recommended values. Secondly, the fraction of O((1)D) quenched to O((3)P) by CH4, k(1q)/k(1), was precisely determined from chemiluminescence decays over the temperature range 236 to 340 K. A temperature independent value for k(1q/)k(1) of 0.002 +/- 0.003 was found. Finally, LIF detection of OH has been applied to accurately determine the product branching fraction to OH of O((1)D) CH(4) at room temperature. Our value, k(1a)/k(1) = 0.76 +/- 0.08 (95% confidence), is in line with recent determinations by other groups.