Theoretical study on the nonadiabatic transitions in the photodissociation of Cl2, Br2, and I2

We have theoretically studied the nonadiabatic transitions among the five lower states with the Ohm=1(u) symmetry (1(u)((1)) to 1(u)((5))) in the photodissociation of Cl-2, Br-2, and I-2 by using the spin-orbit configuration interaction (SOCI) method and the semiclassical time-dependent coupled Schrodinger equations. From the configuration analyses of the SOCI wavefunctions, we found that the nonadiabatic transition between 1(u)((2)) and 1(u)((1)) is a noncrossing type, while that between 1(u)((3)) and 1(u)((4)) is a crossing type for all the molecules. The behavior of the radial derivative coupling element between lu(') and lu(2) and that between 1(u)((1)) and 1(u)((4)) is analyzed in detail. In Cl-2, nonadiabatic transitions can take place even between the states correlating to different dissociation limits, while in Br-2 and I-2, with the usual photon energies e.g. less than 20 eV, nonadiabatic transitions occur only between the states correlating to the same dissociation limits, reflecting the different magnitudes of the spin-orbit interactions.