The E, F 1Σ+g double-minimum state of hydrogen: Two-photon excitation of inner and outer wellsa)

Publisher Website
Google Scholar
Abstract
Low‐lying vibrational levels (v=2 and 3) of the outer well of the double‐minimum E, F 1Σ+g state of molecular hydrogen are experimentally observed for the first time permitting a rotational analysis. The E, F state is excited by two‐photon absorption using tunable (∼195 nm) Raman‐shifted radiation of a frequency‐doubled dye laser. The nonlinear absorption is detected by monitoring the subsequent photoionization of the E, F state. Homogeneous perturbations are observed between the vE=1 and vF=2 levels of the inner and outer wells, respectively. The molecular parameters for these levels (derived by a deperturbation analysis) as well as those for the unperturbed vF=3 level are compared with recent ab initio calculations and small deviations are noted. The rotational intensity distribution of the E–X (0,0) band mirrors the ground state rotational population, whereas the corresponding distributions of the E–X (1,0) and (2,0) bands as well as the F‐X (4,0) band do not follow this pattern. This is interpreted in terms of vibronic coupling between the inner and outer wells of the E, F state. A comparison between the experimental rotationless intensities and those calculated from ab initio ground and excited state vibrational wave functions suggests that photoionization from the outer well is more effective than from the inner well.