ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Ab initio calculated symmetry coordinate and internal valence coordinate coefficients for the two spin–spin coupling surfaces of the silane molecule—1J(Si, H) and 2J(H,H)—are presented. Calculations were carried out at the 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 distinct points on the 1J(Si, H) surface and 177 distinct points on the 2J(H,H) surface. The results were fitted to fourth order in Taylor series expansions and are presented to second order in the coordinates. Both couplings are sensitive to geometry—more so than found for methane in earlier calculations. The surfaces are averaged over a very accurate, recent ab initio force field to give values for the couplings in silane and its variously deuterated isotopomers over a range of temperatures. For J(Si, H) in 29SiH4 both stretching and bending contribute to the nuclear motion effects with the former being considerably larger numerically. For J(H,D) in 28SiH3D the bending and stretching contributions are both substantial but, being of opposing sign, cancel each other out, leaving the bending–stretching cross terms to give most of the remaining contributions. The calculated values are in excellent agreement with new experimental values presented in this work; for 1J(Si, H) in 29SiH4 and 29SiHD3 at 298 K we calculate −199.9 Hz and −198.5 Hz, respectively, to be compared with experimental values of −201.3 (±0.4) Hz and −199.9 (±0.4), Hz respectively. For (γH/γD) J(H,D) we predict a value of 2.58 Hz, to be compared with 2.61 (±0.08) Hz obtained by experiment at 298 K. Calculation of the tensor components of all parts of the one-bond and two-bond couplings are reported 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)〉K⊥ for silane and K(parallel)〈K⊥ for methane. For J(H, H) each component of the contributory parts of the coupling is numerically smaller for silane than for methane. © 2001 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1398091
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