CORRELATED CALCULATIONS FOR THE NUCLEAR MAGNETIC SHIELDINGS OF CO AND HCN

Nuclear magnetic shielding tensors and spin rotation constants are calculated for CO and HCN using both the coupled Hartree-Fock (CHF) and the second-order polarization propagator approximation (SOPPA). For CO we find that SOPPA recovers about half of the difference between CHF and experiments for both nuclei. For HCN there is no effect of SOPPA for H, little for C, but a large effect for N, where the resulting isotropic shielding, sigma-N = -17 ppm, is in good agreement with the most recent experiment. We have also analysed some earlier correlated calculations of shieldings of CO. Isotope effects on the shieldings are reported for CO.