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.

The radiation-induced chemistry in solid xenon matrices

“…A characteristic feature of the EPR spectra of trapped H atoms in solid xenon is extended, complex superhyperfine structure (SHFS) resulting from interaction of unpaired electron with the nuclei of magnetic isotopes ( 129 Xe and 131 Xe). This structure was detected in the pioneering work of Foner et al [48] and reproduced in many other studies, independent of the generation method (photolysis or radiolysis) [8,9,23,[49][50][51]. However, analysis of the structure pattern consisting of large number of anisotropic components in natural xenon was found to be quite complicated, so the trapping site nature for H atoms in solid xenon remained under discussion for a long time [49,50,53,54].…”

Variational Theory of Paramagnetic Impurities in Van der Waals Crystals

“…These specific functions will be introduced late in the calculations, however, so an extension of the work could easily be made with some other choice. )=0 (6)(7)(8)(9)(10)(11) if (23 3) and 01(Sl) are centered on the same nucleus.…”

“…ter m is " " 49 EAf = PAy:-6 CATe-(« 1,1 + 3,«-) + 2 6 0(A (7)(8)(9)(10)(11) which, on keeping only direct terms, becomes…”

“…In this approximation Eqs. (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) and (7-23) become …”

Impurity states in solid neon∗†

“…Magnetic resonance atu-(9),(10), (11) die s of impurity centers tn these materials have also beon performed. (12), (13) L6wdin has reviewed the advances which have been made in treating the ground-states of pure alkall-halide crystals from first principles.…”