Rate Coefficients for the Reactions of Hydroxyl Radicals with Methane and Deuterated Methanes

Abstract

The rate coefficients for the reaction of OH with CH3D (k1), CH2D2 (k2), CHD3 (k3), CD4 (k4), and CH4 (k5) as well as that of OD with CH4 (k6) have been measured using the pulsed photolytic production of OH followed by its detection via pulsed laser induced fluorescence. k1−k4 and k6 were measured between ∼220 and ∼415 K, while k5 was measured down to 195 K. The measured rate coefficients do not strictly obey the Arrhenius expression. However, below 298 K, they can be represented by the expressions (in cm3 molecule-1 s-1): k1 = (3.11 ± 0.44) × 10-12 exp[−(1910 ± 70)/T]; k2 = (2.3 ± 1.2) × 10-12 exp[−(1930 ± 250)/T]; k3 = (1.46 ± 0.22) × 10-12 exp[−(1970 ± 70)/T]; k4 = (1.00 ± 0.22) × 10-12 exp[−(2100 ± 120)/T]; k5 = (1.88 ± 0.11) × 10-12 exp[−(1695 ± 30)/T]; k6 = (1.68 ± 0.12) × 10-12 exp[−(1640 ± 40)/T]. The obtained values of the rate coefficients and kinetic isotope effects are compared with values previously measured or calculated by other groups. The atmospheric implications of this data are briefly...