ROVIBRATIONALLY AVERAGED NUCLEAR MAGNETIC SHIELDING TENSORS CALCULATED AT THE COUPLED-CLUSTER LEVEL

Nuclear magnetic shielding tensor functions for H-2, HF, N-2, CO, and F-2 are calculated at the coupled-cluster singles and doubles level au gmented by a perturbative correction for triple excitations [CCSD(T)]. The shielding constants for the lowest rovibrational states of these diatomics are obtained by solving the rovibrational Schrodinger equati on with the finite-element method. For H, C, and F, absolute scales fo r the nuclear magnetic shielding constants have been obtained by combi ning computed diamagnetic shieldings with paramagnetic contributions d educed from measured spin-rotation constants and calculated rovibratio nal corrections. Since the experimental spin-rotation constants for N- 2 and CO are inaccurate, shielding scales for N and O based on coupled cluster calculations are probably the most accurate available. (C) 19 96 American Institute of Physics.