Coupled cluster study of NMR shielding constants and spin-rotation constants in SiH4, PH3and H2S molecules

Abstract

Ab initio methods are applied to analyse the NMR shielding constants and spin-rotation constants in SiH₄, PH₃ and H₂S molecules. The electron correlation effects are studied applying the MP2 and coupled cluster perturbation approaches. The basis set convergence is examined at the same time, and the final results for the equilibrium geometries are obtained at the CCSD(T)/cc-pCVQZ level. Zero-point vibrational and temperature contributions are computed at the SCF, MP2 and CCSD level of approximation. In addition, for the shielding constants we also estimate the relativistic effects, to determine total values of the shielding of the third-row nuclei in the studied molecules. Our final results for the shielding constants at 300 K are σ (²⁹Si in SiH₄) = 482.35 ppm, σ (³¹P in PH₃) = 611.64 ppm and σ (³³S in H₂S) = 736.13 ppm. These values, together with estimated corrections and error bars, can be used to determine absolute NMR shielding scales for the heavy nuclei.