Pulse radiolysis of alkane/carbon tetrachloride glasses and liquids

The pulse radiolysis of 3-methylpentane (3MP) glasses and liquids, containing CCl/sub 4/ and various electron and positive ion scavengers, was studied at 75, 77, 85, 95, and 123 K. The results are consistent with a mechanism in which CCl/sub 4/ reacts with excess electrons to form CCl/sub 4//sup -/ (lambda/sub max/ = 370 nm) which dissociates into CCl/sub 3/ and Cl/sup -/, followed by positive charge transfer from a cation to produce CCl/sub 3//sup +/ (lambda/sub max/ = 470 nm). At 95 K, the decay of CCl/sub 4//sup -/ and the growth of CCl/sub 3//sup +/ are complete in less than 1 ms. A value of 1.1 x 10/sup 4/ M/sup -1/ cm/sup -1/ was determined for epsilon/sub max/(CCl/sub 4//sup -/) in 3MP/CCl/sub 4/ glasses by measuring the reduction in the yield of trapped electrons which accompanied CCl/sub 4//sup -/ production. The assignment of the 370-nm band to CCl/sub 4//sup -/, rather than CCl/sub 4//sup +/ as commonly accepted, removes some perplexing problems in understanding the radiolysis of cold alkane/CCl/sub 4/ mixtures. A suggestion in the literature that the free radical CCl/sub 3/ has an absorption band at 365 nm is considered to be improbable.