Mechanism of Hydrogen Formation by Electrons in x- or γ-Irradiated Gaseous HCl

Abstract

Studies of the effects of Cl2 and SF6 on the production of hydrogen from the x or γ radiolysis of gaseous HCl indicate that 2.5 ± 0.1 electrons per 100 eV form an intermediate H α , which is not a thermal hydrogen atom. The remainder of the total yield of 4.0 electrons per 100 eV give rise to thermal hydrogen atoms. The results can be explained satisfactorily on the basis of the electron‐capture reactions (6a) and (6c) (see text), where the sum of k 6a and k 6c lies in the range 5 × 10−32 to 2.6 × 10−30 ml2 molecule−2·sec−1. H α is taken to be a clustered form of HCl− which either produces molecular hydrogen in further reactions with HCl molecules, or is scavenged by Cl2. The rate constant ratio k H α +HCl / k H α +Cl 2 was 8 × 10−6 at − 77° ± 2°C and 1.2 ± 0.3 × 10−3 at 1° ± 1°C. Chlorine competes with HCl for the thermal hydrogen atoms formed in Reaction (6a) as well as for H α , and at − 77° ± 2°C k H+HCl / k H+Cl 2 was found to have a value of 2.6 ± 0.7 × 10−3, in good agreement with the data of Klein and Wolfsberg. SF6 cannot scavenge thermal hydrogen atoms and its effects are attributable entirely to a competition with HCl for electrons.