Vibrational averaging of NMR properties for an N-H-N hydrogen bond

Vibrational effects on NMR shielding constants and nuclear spin-spin coupli ng constants have been investigated in a model hydrogen-bonded complex, CNH :NCH. Expectation values of the spin-spin coupling constant (2h)J(N-N), obt ained from a two-dimensional EOM/CCSD/(qzp,qz2p) surface, and of the isotro pic proton shielding constant sigma (H), obtained from a two-dimensional MP 2/(qzp,qz2p), surface, are presented as functions of vibrational state. The expectation values have been computed from anharmonic dimer- and proton-st retching vibrational wavefunctions obtained from a two-dimensional MP2/aug' -cc-pYTZ potential surface. Equilibrium values, ground-state expectation va lues, and thermally averaged values at 298 K of (2h)J(N-N), and sigma (H) a re compared. (C) 2001 Elsevier Science B.V. All rights reserved.