Perturbations in the b 4g- state of O2 + immediately below the predissociation limit, studied by high-resolution optical-optical double-resonance photofragment spectroscopy

Optical-optical double-resonance photofragment spectroscopy of molecular ions is, for the first time, performed with a Doppler-limited resolution of 0.003 cm-1. The high resolution allows the observation of perturbations in the b 4g- state arising from a vibrationally excited level in the d 4g+ state lying only 29 cm-1 below the predissociation limit. The matrix element for the interaction between the b and d states is obtained from a perturbation analysis and is used to estimate the contribution of the d state to the predissociation of the b state. Precise effective Hamiltonians are reported for the a 4 u(v=4,5) and b 4g-(v=4) states.