RATE COEFFICIENTS FOR THE REACTIONS OF HYDROXYL RADICALS WITH METHANEAND DEUTERATED METHANES

The rate coefficients for the reaction of OH with CH3D (k(1)), CH2D2 ( k(2)), CHD3 (k(3)), CD4 (k(4)), and CH4 (k(5)) as well as that of OD w ith CH4 (k(6)) have been measured using the pulsed photolytic producti on of OH followed by its detection via pulsed laser induced fluorescen ce. k(1)-k(4) and k(6) were measured between similar to 220 and simila r to 415 K, while k(5) was measured down to 195 K. The measured rate c oefficients do not strictly obey the Arrhenius expression. However, be low 298 K, they can be represented by the expressions (in cm(3) molecu le(-1) s(-1)): k(1) = (3.11 +/- 0.44) x 10-(12) exp[-(1910 +/- 70)/T]; k(2) = (2.3 +/- 1.2) x 10(-12) exp[-(1930 +/- 250)/T]; k(3) = (1.46 /- 0.22) x 10(-12) exp[-(1970 +/- 70)/T]; k(4) = (1.00 +/- 0.22) x 10( -12) exp[-(2100 +/- 120)/T]; k(5) = (1.88 +/- 0.11) x 10(-12) exp[-(16 95 +/- 30)/T]; k(6) = (1.68 +/- 0.12) x 10(-12) exp[-(1640 +/- 40)/T]. The obtained values of the rate coefficients and kinetic isotope effe cts are compared with values previously measured or calculated by othe r groups. The atmospheric implications of this data are briefly discus sed.