Theoretical study of nonadiabatic transitions in the photodissociation of Cl₂ and Br₂

Lower-lying potential curves of Br₂ are calculated by the spin-orbit configuration interaction method, and the spin-orbit branching mechanisms in the photodissociation processes are examined. The second absorption band at 227 nm is assigned unambiguously to the transition from the X¹Σ⁺_g to the ³Σ⁺_1u (σ_g→σ_u* state. The calculated potential curves and the radial derivative coupling elements of Cl₂ and Br₂ are used to evaluate the nonadiabatic transition probabilities by solving the time-dependent coupled Schrödinger equations semiclassically. The different nonadiabatic behavior in Cl₂ and Br₂ is analyzed in terms of the differences in the electronic factors and the reduced mass.