Spin-orbit branching ratios for the Cl atom photofragments following the excitation of Cl2 from 310 to 470 nm

Velocity distributions for the Cl(P-2(3/2)) and Cl(P-2(1/2)) photofragments produced by photolysis of Cl-2 in the region between 310 and 470 nm are measured using photofragment velocity mapping. Our results indicate that at short wavelengths the absorption spectrum is dominated by the 1(u) ((1)Pi(u)) excited electronic state which produces two ground state chlorine atoms. The O-u(+) (B (3)Pi(u)) state which produces a spin-orbit excited and a ground state chlorine atom becomes significant at 350 nm and dominates the spectrum beyond 400 nm. Analysis of the photofragment angular distributions indicates that the Cl(P-2(3/2)) photofragments are aligned and the magnitude of the alignment is quantitatively determined. Nonadiabatic curve crossing between the 1(u) ((1)Pi(u)) and the O-u+ (B (3)Pi(u)) electronic states is observed and quantified below 370 nm. The measured nonadiabatic transition probability is modeled using the Landau-Zener formula and the position of the curve crossing is estimated at similar to 3 eV above the zero-point of ground electronic state of Cl-2. (C) 1999 American Institute of Physics. [S0021-9606(99)01510-X].