Oriented chlorine atoms as a probe of the nonadiabatic photodissociation dynamics of molecular chlorine

Molecular chlorine was photolyzed using circularly polarized radiation at 3 10 and 330 nm, and orientation moments of the chlorine-atom Cl(P-2(j)) phot ofragment distributions were measured by resonance enhanced multiphoton ion ization using circularly polarized light with Doppler resolution. The produ ct atoms were found to be strongly oriented in the laboratory as a result o f both incoherent and coherent dissociation mechanisms, and the orientation moments contributed by each of these mechanisms have been separately measu red. The experimental results can be explained by nonadiabatic transitions from the C (1)Pi (1u) state to higher states of Omega =1(u) symmetry, induc ed by radial derivative coupling. Ab initio calculations indicate strong Ro sen-Zener-Demkov noncrossing-type radial derivative couplings between state s of 1(u) symmetry. The observed angular distribution (beta parameter) indi cates that 88% of Cl*(P-2(1/2)) fragments produced at 310 nm originate from a perpendicular transition to the C state. The orientation measurements su ggest that 67 +/- 16% of Cl-35*(P-2(1/2)) atoms dissociate via the 1(u)((3) Sigma (+)(1u)) state, and 21 +/-6% dissociate via the 1(u)((3)Delta (1u)) s tate. (C) 2000 American Institute of Physics. [S0021-9606(00)01444-6].