Identification of Excited Gerade States of Molecular Hydrogen with Extreme Ultraviolet-Visible Double Resonance Excitation Technique

Abstract

Extreme ultraviolet-visible double resonance excitation has been employed to populate selected rovibronic levels of the EF 1Σg+, H 1Σg+, I 1Πg and J 1Δg states of H2 lying in the range between 115,000 and 117,600 cm-1 above the ground state X 1Σg+. Tunable coherent extreme ultraviolet radiation, generated by a four-wave mixing process in Xe, prepares H2 in the intermediate B 1Σu+ (v = 6, J) state. Subsequent absorption of the visible laser radiation brings H2 to the higher gerade states and the fluorescence light from these states is detected. Term values of 41 rovibronic levels in these gerade states, including 23 previously unidentified levels, were determined. The single rovibronic fluorescence lifetimes were also measured under the collision-free condition. The fluorescence lifetimes of the EF 1Σg+ states exhibited significant rotational dependences. The nonadiabatic coupling among the adiabatic upper gerade vibronic states explained the observed rotational dependences successfully.