GROWTH AND DECAY PROPERTIES OF TRAPPED H-ATOMS AND D-ATOMS PRODUCED BY THE PHOTOLYSIS OF HI, DI, AND HBR IN 3MP-D14 GLASS - EVIDENCE FOR TUNNELING ABSTRACTION OF D FROM C-D BONDS BY H-1

Earlier results on the production of trapped hydrogen atoms (Htr) by the 254-nm photolysis of HI in 3-methylpentane-d14 (3MP-d14) glass at <50 K, and on their decay, have been extended and elucidated. The profiles of growth of Htr and trapped radicals have been explained and the mechanism for the concurrent production of Dtr. has been assigned. The 254-nm photolysis of DI and the 185-nm photolysis of HBr in 3MP-d14 at <50 K produce trapped D and H atoms with yields and decay properties similar to Htr produced from HI. The composite first-order decay of Htr, which is observable from 4 to 50 K on the seconds time scale and for which the fractional decay rates are independent of the initial concentrations of H, I, HI, and radicals, has an activation energy of <50 cal mol-1. The evidence strongly indicates that the rate-determining step in decay is tunneling abstraction of D from C-D bonds by Htr. © 1979 American Chemical Society.