Electron-induced delayed desorption of solid argon doped with methane

The total yield of particles desorption from solid Ar doped with CH₄ under irradiation with an electron beam was studied at 5 K. The measurements were carried out at a CH₄ concentration of 1 and 5%. The effect of explosive delayed desorption from the surface of argon matrix was discovered in both mixtures. With a higher concentration of CH₄, it appeared at lower doses and was more pronounced. Two types of self-oscillations were observed: long-period bursts (on a time scale of about 25 min) and short-period oscillations (of about 10 s). In pure solid Ar delayed desorption was not observed despite the accumulation of a significant number of excess electrons, exceeding their number in mixtures of Ar and CH₄ as it was found by measurements of thermally stimulated exoelectron emission. This finding discards the model of Coulomb explosion for the phenomenon detected. In this paper we focused on the role of hydrogen (one of the radiolysis products) in delayed desorption. The formation of atomic hydrogen in the matrix was traced via cathodoluminescence by the emission band of the excimer Ar₂H∗ at 166 nm. Desorption of excited hydrogen atoms in the excited state was detected by the Ly-α emission line. A decrease of the Ar₂H∗ band intensity at higher concentration of CH₄ was found evidencing bleaching these centers likely due to recombination of H atoms with energy release and formation of molecular hydrogen. The data obtained give additional evidence in favor of the hypothesis that the exothermic reactions of radiolysis products serve as a stimulating factor for delayed desorption.