Vibrational structure of an electrostatically bound ion–water complex

Supersonically cooled VH2O+ is resonantly one-photon dissociated in the visible region. An excited state vibrational progression in the V+(OH2) stretching mode is observed with a frequency W′e=339 cm−1 and an anharmonicity We X′e =4.5 cm−1. Analysis of the spectra of isotopically substituted species places an estimate of the ground state ion–water stretch at 420±75 cm−1. The electronic origin of the upper state places a strict upper limit to the adiabatic binding energy of this complex at 1.97 eV.