Kinetic isotope effect for the reaction of H atoms with GeH4 and GeD4

Abstract

Rate constants for H atom attack on GeH 4 and GeD 4 have been measured in pulsed photolysis experiments in which H atoms were produced by the mercury-sensitized photolysis of H 2 and monitored by Lyman-␣ absorption. The values obtained for GeD 4 in the temperature range 293 -550 K may be represented by the expressionCombination of the rate constants for GeH 4 measured in this work with those previously determined in this laboratory gives, for the temperature range 293 -455 K,The kinetic isotope effect indicated by these expressions is given bywhich yields k H /k D ϭ 2.0 Ϯ 0.4 at 300 K. This is the first determination of the kinetic isotope effect for radical attack on a Ge 9 H bond.The present results for the reaction of H atoms with GeH 4 have been combined with previously reported data, and the best value for the rate constant over the temperature range 210 -473 K is recommended to be k H ϭ (1.18 Ϯ 0.08) ϫ 10 Ϫ10 exp[(Ϫ 981 Ϯ 22)/ T]