STATE SELECTIVE REACTIONS PREPARED THROUGH THE EXCITATION OF ORBITAL STATES IN VANDERWAALS COMPLEXES OF CA-HX-STAR

We have observed the chemiluminescent reaction Ca* + HX --> CaX* + H, where the reactants are prepared in a van der Waals complex formed in a supersonic expansion. This preparation, combined with tunable laser excitation, allows access to well-defined electronic states of the reaction complex corresponding to different orientations of the calcium excited orbital. In the case of the Ca-HBr complex, a remarkable effect of this preparation is observed on the branching ratio to the final excited states A 2-PI and B 2-SIGMA of CaBr: Depending upon the selected state of the complex, the A/B ratio varies by a factor of 2. This is interpreted by the conservation of the orbital orientation during the reaction involving the departure of the hydrogen.