Collision-Induced intensity of the b1Σg+a1Δg transition in molecular oxygen: Model calculations for the collision complex O2 + H2



Ab initio configuration interaction (CI) calculations have been performed for the O2 + H2 complex in a trapezoidlike collision arrangement with C2v symmetry. The potential energy surfaces of the four lowest states of this van der Waals complex (arising from the X3 Σg, a1 Δg, and b1 Σg+ states of the oxygen moiety), as well as the collision-induced b1 Σg+a1 Δg electric dipole transition moment (Mba), 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 H2(X1 Σg+) + O2(X3 Σg). The geometry optimized at the ROHF/6–311G** 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 b1 Σg+ state (2.96 kJ/mol) in comparison with the a1 Δg (2.1 kJ/mol) and ground X3 Σg states (1.35 kJ/mol) presumably could be explained as resulting from charge-transfer interactions. A good convergence of the calculated transition moment Mba for the larger CI expansions (approximately 50,000 configuration-state functions) has been obtained. The calculated collision-induced intensity of the b1 Σg+-a1 Δg and a1 ΔgX3 Σg transitions in molecular oxygen are in reasonable agreement with recent experimental data for several foreign gases. © 1994 John Wiley & Sons, Inc.