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

Vibrational effects on NMR shielding constants and nuclear spin–spin coupling constants have been investigated in a model hydrogen-bonded complex, CNH:NCH. Expectation values of the spin–spin coupling constant 2hJN–N, obtained from a two-dimensional EOM–CCSD/(qzp,qz2p) surface, and of the isotropic proton shielding constant σH, obtained from a two-dimensional MP2/(qzp,qz2p) surface, are presented as functions of vibrational state. The expectation values have been computed from anharmonic dimer- and proton-stretching vibrational wavefunctions obtained from a two-dimensional MP2/aug′-cc-pVTZ potential surface. Equilibrium values, ground-state expectation values, and thermally averaged values at 298 K of 2hJN–N and σH are compared.