Comparison of semiempirical and ab initio absolute probabilities of rovibronic transitions for the I1Πg-,J1Δg- → C1Πu± system of bands of the H2 molecule

The absolute values of probabilities of the I(1)Pi(g)(-), v', J'; J(1)Delta(g)(-), v', J --> C(1)Pi(u)(+/-), v ", J " spontaneous transitions in the H-2 molecule (for the vibrational and rotational quantum numbers v' = v " = 0-3, J = 1-6, and J " = J, J +/- 1) are calculated by using ab initio and semiempirical data on the dipole moments of the 3d pi(1)Pi(g), 3d delta(1)Delta(g) --> 2p pi(1)Pi(u) electronic transitions. In both cases, the calculations are performed both in the adiabatic approximation and with an allowance for the nonadiabatic effect of electronic-rotational interaction. The coefficients of expansion of the wave functions of perturbed rovibronic states in the Born-Oppenheimer basis functions used in the calculations were obtained in the approximation of purl precession from experimental values of the terms. It was found that the values of transition probabilities based on the ab initio calculations systematically exceed the corresponding semiempirical data by a factor of 1.2-1.9 for the I(1)Pi(g) --> C(1)Pi(u)(+/-) transition and by a factor of 1.4-1.6 for the J(1)Delta(g)(-) --> C(1)Pi(u)(+/-) transition. It was established that the difference between the ab initio and semiempirical values of electronic transition moments virtually has no effect on the dependence of the transition probabilities on the vibrational quantum numbers. The discrepancies between the results of adiabatic and nonadiabatic calculations are significant and reach two orders of magnitude, which is indicative of the important role of perturbations in the probabilities of the transitions considered. (C) 2000 MAIK "Nauka/Interperiodica".