Theoretical study on the nonadiabatic transitions in the photodissociation processes of Cl₂

Photodissociation of Cl₂ on the shorter wavelength side of the first absorption band has been known to yield a small but significant amount of Cl(²P_1/2) from the C ¹∏_u state, despite its adiabatic correlation to the two Cl(²P_3/2) atoms. We calculated some potential energy curves of the ground and excited states of Cl₂ by the spin-orbit configuration interaction method and examined the possibilities of several nonadiabatic transition mechanisms. It was found that the radial Rosen-Zener-Demkov (RZD)-type nonadiabatic transition from the C ¹∏_u to the third Ω = 1_u (³Σ⁺ _1u (σ_g → σ*_u)) state is responsible for the production of Cl(²P_1/2), and the rotational nonadiabatic transition probability from the C ¹∏_u to the B ³∏_0+u state is negligibly small. The wavelength dependence of the product branching ratio Cl(²P_1/2)/Cl(²P_3/2) and the anisotropy parameter β(Cl(²P_1/2)), which was calculated from the electronic transition moments to the A ³∏_1u, B ³∏_0+u, and C ¹∏_u states with the RZD transition mechanism, was in good agreement with their experimental behavior. This RZD model and Young's double slit model could also reproduce the quantum-mechanical interference pattern in the orientation of the total angular momentum J = 1/2 of the products Cl(²P_1/2).