Trapping sites of hydrogen atoms in solid HD and D-2: An electron spin echo study

Trapping sites of H and D atoms in solid HD and D-2 have been determined us ing electron spin echo (ESE) 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 th e 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 i s 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 D+DH --> D-2+H with the increase in temperature in solid HD reported in Chem. Phys. Lett. 261, 463 (1996). (C) 1999 American I nstitute of Physics. [S0021-9606(99)00348-7].