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 Ω=1_u symmetry (1_u⁽¹⁾ to 1_u⁽⁵⁾) in the photodissociation of Cl₂, Br₂, and I₂ by using the spin-orbit configuration interaction (SOCI) method and the semiclassical time-dependent coupled Schrödinger 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 1_u⁽¹⁾ and 1_u⁽²⁾ and that between 1_u⁽³⁾ and 1_u⁽⁴⁾ is analyzed in detail. In Cl₂, nonadiabatic transitions can take place even between the states correlating to different dissociation limits, while in Br₂ and I₂, 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.