The vibrational and temperature dependence of the indirect nuclear spin–spin coupling constants of the oxonium (H3O+) and hydroxyl (OH−) ions Original Research Article

The indirect nuclear spin–spin coupling constants of the gas phase oxonium (H3O+) and hydroxyl (OH−) ions, their temperature dependence and isotope shifts are predicted by ab initio calculations. The coupling constants are calculated as a function of the symmetric stretching and the inversional coordinates of H3O+ and as a function of the bond length of OH− at the uncorrelated level of the random phase approximation (RPA), at the correlated levels of the second order polarization propagator approximation with coupled cluster singles and doubles amplitudes – SOPPA(CCSD) – and of the multiconfigurational random phase approximation (MCRPA) with a large complete active space wavefunction. Effective ro-vibrational state dependent coupling constants are obtained from these functions and the corresponding ro-vibrational wavefunctions. The effective coupling constants for several states are then used to determine the temperature dependence of the coupling constants. The results are compared with the coupling constants of H2O and the nuclear magnetic shielding constants of H3O+ and OH−.