Nuclear spin-spin coupling in silane and its isotopomers: Ab initio calculation and experimental investigation

Ab initio calculated symmetry coordinate and internal valence coordinate co efficients for the two spin-spin coupling surfaces of the silane molecule-( 1)J(Si, H) and (2)J(H,H)-are presented. Calculations were carried out at th e level of the second-order polarization propagator approximation involving coupled-cluster singles and doubles amplitudes [SOPPA(CCSD)] using a large basis set for a total of 78 different geometries corresponding to 133 dist inct points on the (1)J(Si, H) surface and 177 distinct points on the (2)J( H,H) surface. The results were fitted to fourth order in Taylor series expa nsions and are presented to second order in the coordinates. Both couplings are sensitive to geometry-more so than found for methane in earlier calcul ations. The surfaces are averaged over a very accurate, recent ab initio fo rce field to give values for the couplings in silane and its variously deut erated isotopomers over a range of temperatures. For J(Si, H) in (SiH4)-Si- 29 both stretching and bending contribute to the nuclear motion effects wit h the former being considerably larger numerically. For J(H,D) in (SiH3D)-S i-28 the bending and stretching contributions are both substantial but, bei ng of opposing sign, cancel each other out, leaving the bending-stretching cross terms to give most of the remaining contributions. The calculated val ues are in excellent agreement with new experimental values presented in th is work; for (1)J(Si, H) in (SiH4)-Si-29 and (SiHD3)-Si-29 at 298 K we calc ulate -199.9 Hz and -198.5 Hz, respectively, to be compared with experiment al values of -201.3 (+/-0.4) Hz and -199.9 (+/-0.4), Hz respectively. For ( gamma (H)/gamma (D)) J(H,D) we predict a value of 2.58 Hz, to be compared w ith 2.61 (+/-0.08) Hz obtained by experiment at 298 K. Calculation of the t ensor components of all parts of the one-bond and two-bond couplings are re ported for equilibrium geometry and compared to newly calculated values of the corresponding components of methane. The principal finding for the one- bond coupling is that K-parallel to>K-perpendicular to for silane and K-par allel to<K-perpendicular to for methane. For J(H, H) each component of the contributory parts of the coupling is numerically smaller for silane than f or methane. (C) 2001 American Institute of Physics.