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 (σg→σu*) 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.