NMR shielding constants in SeH2 and TeH2

Abstract

Ab initio values of nuclear magnetic resonance shielding constants in SeH2 and TeH2 are calculated. We analyse the role of electron correlation, the magnitude of relativistic effects, the dependence of these results on the basis set and, in addition, the rovibrational effects. The relativistic effects on the isotropic shielding constants calculated with the Dirac–Coulomb Hamiltonian at the Hartree–Fock and Spin-Density Functional Theory levels are very similar, and the electron correlation effects are much smaller. For both molecules, however, the electron correlation contribution to the anisotropy of the heavy atom shielding is much more significant than for the isotropic constant. The total shielding constants derived by adding to the non-relativistic coupled-cluster values the Dirac–Hartree–Fock values of the relativistic effects, σ300 K iso(Se) = 2447 ppm and σ300 K iso(Te) = 4809 ppm, may be applied to define the absolute shielding scales for these heavy nuclei.