Theory of chemical reactions of vibronically excited H2(B 1Σ+u). I. Prediction of a strongly bound excited state of H4

MRD–CI calculations were carried out on the potential energy surfaces of the ground and first excited singlet of the same symmetry of H4, which predict a bound excited state with respect to H2+H*2 (B 1Σ+u) of 3.1 eV at a geometry of trigonal pyramid. This geometry was predicted theoretically according to a model of chemical bonding for ‘‘maximum ionicity excited states.’’ At the minimum and the three dimensional space surrounding it, there is a near touching of the excited with the ground state hypersurfaces. This fact has implications for the spectroscopy and photochemistry of the H2+H*2 system.