The study of the fifth 1Σu+ state (5pσ) of H2: Transition probabilities from the ground state, natural line widths and predissociation yields

The full vibrational progression of the 5pσ 1Σu+ state of H2 was identified in a high-resolution absorption measurement. More than 40 new lines have been assigned in the spectrum. The transition probabilities, the widths and the dissociation yields for rovibronic lines with J″ = 0…3 of the various absorption bands of the fifth (5pσ) 1Σu+ state out of the X1Σg+v″=0 ground state were measured over the complete vibrational progression. Predissociation was found to be an efficient de-excitation channel for these levels. The predissociation yields and the dissociation widths were measured for nearly the complete vibrational progression. Resonances of the 5pσ1Σu+ state in the H(n = 3) + H(1s) continuum were observed for the first time. Calculations show that they are located behind a large potential barrier. The comparison between the absolute values of these transition probabilities with the calculated values demonstrates clearly the importance of non-adiabatic couplings ignored in the calculations.