Growth and decay properties of trapped hydrogen and deuterium atoms produced by the photolysis of hydriodic acid, hydriodic acid-d, and hydrobromic acid in 3MP-d14 glass. Evidence for tunneling abstraction of deuterium from carbon-deuterium bonds by hydrogen

Abstract

Earlier results on the production of trapped hydrogen atoms (H/sub tr/) by the 254-nm photolysis of HI in 3-methylpentane-d/sub 14/ (3MP-d/sub 14/) glass at < 50 K, and on their decay, have been extended and elucidated. The profiles of growth of H/sub tr/ and trapped radicals have been explained and the mechanism for the concurrent production of D/sub tr/ has been assigned. The 254-nm photolysis of DI and the 185-nm photolysis of HBr in 3MP-d/sub 14/ at < 50 K produce trapped D and H atoms with yields and decay properties similar to H/sub tr/ produced from HI. The composite first-order decay of H/sub tr/ which is observable from 4 to 50 K on the seconds time scale for which the fractional decay rates are independent of the initial concectrations of H, I, HI, and radicals, has an activation energy of < 50 cal mol/sup -1/. The evidence strongly indicates that the rate-determining step in decay is tunneling abstraction of D from C-D bonds by H/sub tr/. 5 figures.