Mechanism of Hydrogen Formation in the Radiolysis of n-Pentane

Abstract

The radiolytic yields of trichloroethylene, hydrogen, and hydrogen chloride from solutions of tetrachloroethylene in n-pentane were determined. A mechanism for radiolytic hydrogen formation, which assumes the existence of three precursors of hydrogen, is postulated. The initially formed excited species C5H12′ is assumed to yield thermal hydrogen atoms. This species is scavenged at low tetrachloroethylene concentrations. Molecular (unscavengeable) hydrogen is assumed to be formed from the decomposition of another excited species, C5H12″, a process which is not affected by the presence of tetrachloroethylene. Hot hydrogen atoms are assumed to be formed mainly from charge recombination reactions. The reduction in hydrogen yield at concentrations above 10−2M tetrachloroethylene is due predominantly to electron scavenging by the solute. Kinetic treatment of the results gives the following G values for the hydrogen yield resulting from the decomposition of C5H12′ and C5H12″ and from charge recombination reactions: G(H) thermal = 1.0; G(H2) molecular = 1.6; G (H2) electronic = 2.3.