Multiple Trapping Sites for Hydrogen Atoms in Rare Gas Matrices

Abstract

Hydrogen atoms have been stabilized in nonequivalent lattice sites in matrices of the rare gases at liquid helium temperature. Electron spin resonance spectra of H atoms in argon, krypton, and xenon show that at least two trapping sites are involved in each case. In a neon matrix, H atoms have been stabilized in only one site. Attainability of the various trapping sites apparently depends on the initial energy of the H atom, a simple doublet spectrum being obtained when the atoms are deposited from the gas phase, while multiple trapping spectra are obtained when the atoms are produced by photolysis in the solid. The hyperfine coupling contants and the electronic g factors for H atoms trapped in the various matrix sites have been determined. The deviation of the hyperfine coupling constant from the free‐state value is positive in some cases and negative in others. The experimental results are in good agreement with theoretical predictions. A complex multicomponent H atom spectrum was obtained by photolysis of HI in xenon. The subsplitting in the spectrum is attributed to magnetic hyperfine interactions with matrix nuclei (Xe¹²⁹ and Xe¹³¹). The nature of the trapping sites in rare gas matrices is discussed. Evidence for trapping in substitutional sites and octahedral sites is presented.