Spectroscopic evidence on the absence of trapped chemical dimer cations (1) after irradiation of n-pentane in the solid state

Abstract

Absorption spectra were recorded after irradiation of a number of decane isomers in n-pentane and 3-methylpentane (with CO 2 added as electron acceptor) and in 1,1,2-trichlorotrifluoroethane at 77 K. Absorption bands, with band maxima ranging from 595 to 760 nm were observed in all cases, except after irradiation of 2,6-, 3,5- and 3,6-dimethyloctane and 3,4-diethylhexane in pentane and after irradiation of n-decane and 3,4-diethylhexane in 3-methylpentane. No absorption in the same spectral region was observed after irradiation of pentane with CO 2 or 2-chlorobutane added as electron acceptor. The results specifically rule out the presence of trapped condensation ions, formed by “direct dimerization” (RH + + RH → R + 2 + H 2) or pentane cations with pentane molecules, after irradiation of pentane at 77 K. Arguments against direct “ionic dimerization” in the radiolysis of alkanes are presented and discussed.