Molecular beam photoelectron spectroscopy and femtosecond intramolecular dynamics of H2O+ and D2O+

Abstract

The 584 Å photoelectron spectra of supersonic molecular beams of H₂O and D₂O have been obtained with improved resolution. The spectroscopic constants of the X̃ ²B₁ and à ²A₁ state ions, including ω⁰₁, x⁰₁₁, ω⁰₂, x⁰₂₂, and x⁰₁₂, are reported. For the first two electronic states of the ion, precise line splittings were evaluated with a least squares fitting procedure, employing sums of empirical instrument response functions and a linear background. A simulation of the vibrational manifolds of the B̃ ²B₂ state ions with combination progressions in the symmetry‐allowed modes ν₁ and ν₂ failed to reproduce the diffuse photoelectron bands observed for both H₂O and D₂O. Autocorrelation functions were calculated from the photoelectron bands of all three electronic states. The B̃ ²B₂ state correlation functions exhibit ultrafast decay, occurring on a 10⁻¹⁴ s time scale. The ν₂ motion appears to define the decay in the correlation function. This behavior supports a previously proposed B̃ ²B₂–à ²A₁ curve‐crossing model for the nonradiative relaxation of the B̃ ²B₂ state ions.