Collision‐Induced intensity of the b 1 Σ g + − a 1 Δ g transition in molecular oxygen: Model calculations for the collision complex O 2 + H 2

Ab initio configuration interaction ( CI ) calculations have been performed for the O 2 + H 2 complex in a trapezoidlike collision arrangement with C 2 v symmetry. The potential energy surfaces of the four lowest states of this van der Waals complex (arising from the X 3 Σ g − , a 1 Δ g , and b 1 Σ g + states of the oxygen moiety), as well as the collision‐induced b 1 Σ g + − a 1 Δ g electric dipole transition moment ( M b – a ), have been analyzed for different CI expansions, using as a reference determinant the restricted open‐shell Hartree–Fock ( ROHF ) function for the ground state of the complex H 2 ( X 1 Σ g + ) + O 2 ( X 3 Σ g − ). The geometry optimized at the ROHF /6–311 G ** level was refined by a partial optimization at the CI level scanning the intermolecular distance. The equilibrium distances for the X , a , and b states have been found to be a slightly different in the region 3.02–2.98 Å. The larger binding energy of the b 1 Σ g + state (2.96 kJ/mol) in comparison with the a 1 Δ g (2.1 kJ/mol) and ground X 3 Σ g − states (1.35 kJ/mol) presumably could be explained as resulting from charge‐transfer interactions. A good convergence of the calculated transition moment M b – a for the larger CI expansions (approximately 50,000 configuration‐state functions) has been obtained. The calculated collision‐induced intensity of the b 1 Σ g + ‐ a 1 Δ g and a 1 Δ g − X 3 Σ g − transitions in molecular oxygen are in reasonable agreement with recent experimental data for several foreign gases. © 1994 John Wiley & Sons, Inc.