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

Photodissociation of Cl-2 on the shorter wavelength side of the first absorption band has been known to yield a small but significant amount of Cl(P-2(1/2)) from the C (1)Pi (u) state, despite its adiabatic correlation to the two Cl(P-2(3/2)) atoms. We calculated some potential energy curves of the ground and excited states of Cl-2 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)Pi (u) to the third Omega = 1(u) ((3)Sigma (+)(1u) (sigma (g) --> sigma (u)*)) state is responsible for the production of Cl(P-2(1/2)), and the rotational nonadiabatic transition probability from the C (1)Pi (u) to the B (3)Pi (0+u) state is negligibly small. The wavelength dependence of the product branching ratio Cl(P-2(1/2))/Cl(P-2(3/2)) and the anisotropy parameter beta (Cl(P-2(1/2))), which was calculated from the electronic transition moments to the A (3)Pi (1u), B (3)Pi (0+u), and C (1)Pi (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(P-2(1/2)).