Trapping sites of hydrogen atoms in solid HD and D2: An electron spin echo study

Abstract

Absence of recombination of neighboring H atoms in highly purified solid parahydrogen: Electron spin resonance, electron-nuclear double resonance, and electron spin echo studies Trapping sites of H and D atoms in solid HD and D 2 have been determined using electron spin echo ͑ESE͒ spectroscopy. It was found that all the H and D atoms are trapped in substitutional sites and that the H atoms push back surrounding HD(D 2 ) molecules to produce local lattice distortion around the atoms, whereas the D atoms do not. It is expected that the local lattice distortion is produced by zero-point motion of the H atoms whose amplitude is larger than that of host HD(D 2 ) molecules and that the isotope effect is due to difference in the amplitude between the H and D atoms. The lattice distortion around the H atoms may induce the increase in rate constant for the tunneling reaction DϩDH→D 2 ϩH with the increase in temperature in solid HD reported in Chem.

Tunneling chemical reactions D+H2→DH+H and D+DH→D2+H in solid D2–H2 and HD–H2 mixtures: An electron-spin-resonance study

“…22 Since the intermolecular distance in solid hydrogens is close to equilibrium distance in the linear hydrogen atom-molecule van der Waals complex ͑ϳ3.5 Å͒, 1 D and H atoms in solid HD and D 2 are trapped in the substitutional site with a very small cage distortion ͑0 -0.2 Å͒. 16 For these reasons, the hydrogen molecules which surround reactants should play a minor role on these reactions in solid hydrogens.…”

“…It has been found by electron-nuclear double resonance ͑ENDOR͒ and electron-spin-echo ͑ESE͒ studies that all hydrogen atoms produced by the radiolysis are trapped in substitutional site of solid hydrogens due to self-annealing effect. [15][16][17] Therefore, the D and H atoms produced by photolysis were also found to be trapped in substitutional sites of solid hydrogens. The coincidence in ⌬H also indicates that the distance between D ͑H͒ and I atoms dissociated by the photolysis is more than 20 Å estimated by dipole-dipole interaction between paramagnetic species of D ͑H͒ and I atoms.…”

EPR Study of H and D Atoms in Quench-Condensed Solid D $$_{2}$$ 2

“…In turn, the D atoms in solid D 2 do not disturb the substitutional site. This effect was suggested [10] to come from difference in the zero-point motion amplitude for the trapped H and D atoms. Probably, the pushing back matrix molecules contribute in part to the isotope effect in the HFSC matrix shift found previously for H and D in solid D 2 [25,26].…”

“…The table also provides the matrix particle polarizabilities, α, and the nearest neighbor distances for a perfect lattice, R 0 . It is worth noting here the isotope effect in the nearest neighbor distance measured by Kumada et al [10] for H and D in solid hydrogens, H 2 , HD, and D 2 . There experimental results indicate that the H atoms are trapped in the substitutional sites in HD, H 2 , and D 2 and push back surrounding matrix molecules by 0.17 Å in HD and by 0.15 Å in D 2 .…”

“…Different kinds of irradiation were also employed. Among them: exposition of solid hydrogens to the cobalt-60 source irradiation [7,8], preparation of samples of D atoms matrix isolated in D 2 by freezing a mixture of a large amount of deuterium with a small amount of tritium at a low-temperature surface [1,9], production of H and D atoms in solid HD and D 2 by X-ray radiolysis of solid D 2 − H 2 (2 mol%) mixture [10]. Gordon et al [11] and later Bernard et al [12,13] used a technique of sample preparation that differs considerably from those described above.…”