Formation of metastable atomic hydrogen in the 2s state from symmetry-resolved doubly excited states of molecular hydrogen

The cross sections for the formation of the metastable atomic hydrogen in the 2s state in photoexcitation of H₂ and D₂ were measured as a function of the incident photon energy in the range of the doubly excited states with their symmetries of the electronic states, 1Σu+ or 1Π_u, being resolved. It has turned out from the comparison with the cross-section curves for other dissociation processes and the theoretical calculation that the Q₂1Π_u(1) doubly excited state of H₂ dissociates into both H(2s) + H(2p) and H(2p) + H(2p). The dissociation dynamics of this state has been discussed in terms of the nonadiabatic transition during neutral dissociations.