Electric field gradient antishielding for HD and D-2 - art. no. 165201

We calculate the electric field gradient (efg) antishielding factors for th e nuclei of HD and D-2 in their J = 0 and J = 1 states using perturbation t heory. For J = 1, the factor depends on the m(j) state. Since the antishiel ding factor is quite large, the effective efg felt by the nuclei can be mor e than an order of magnitude greater than the bare efg on, say, an H atom. Combined with NMR results on deuterium nuclei, this yields a compelling arg ument that the isolated molecular hydrogen in a-Si:H(D) resides in sites of approximate cubic symmetry, such as the amorphous analogue of tetrahedral sites. We also report on a variational calculation fur axial field gradient s of arbitrary magnitude.