Theory of chemical reactions of vibronically excited H2(B 1Σ+u). II. Noble gas dihydrides

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Abstract
The recently discovered chemically bound excited state of HeH2 from large MRD–CI calculations can be explained in terms of the highly ionic character of the H2B 1Σ+u excited state at R=4.0 a.u. and the resulting binding between it and the polarized He via electrostatic and overlap (with the diffuse ‘‘H −’’ center) effects. Based on this explanation, a theory for chemical reactions of normally nonreactive systems is proposed. These reactions may occur when one of the reacting molecules is excited vibronically to a state of maximum ionicity. The H2B 1∑+u state presents a convenient test case. State‐specific, open shell SCF calculations have been carried out for the He+H*2, Ne+H*2, and Ar+H*2 systems. The results for He+H*2 agree with the MRD–CI calculations and demonstrate that electron correlation is reasonably constant over the potential energy surface. NeH*2 and ArH*2 molecules are predicted for the first time to bind chemically in an excited 1A′ state at geometries similar to HeH*2 and close to a crossing with the unbound ground state into which they can decay radiatively or via nonadiabatic coupling. Our results suggest that, in accordance with the previous observations by Fink et al. [J. Chem. Phys. 5 6, 900 (1972)] of quenching of fluorescence of the H2B 1Σ+u→X 1Σ+g transition in a He+H*2 system, quenching should be observed in Ne+H*2 and Ar+H*2 systems, but this time for higher vibrational numbers.

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