Selective rotational energy transfer from individual Λ-doublet levels of highly rotationally excited CN(A2II)

Optical-optical double resonance was employed to investigate inelastic transitions between highly rotationally excited CN(A(2)II) Lambda-doublet, fine-structure levels, induced by collisions with argon. Rotationally excited CN was prepared by 193 nm photolysis of BrCN diluted in Ar at total pressure similar to 1 Torr. Dramatically different final state distributions were observed for initial Lambda-doublet levels of A' and A " symmetry. These propensities are believed to arise from approach in a 'helicopter' orientation on the more attractive Ar-CN(A) A' potential energy surface, followed by curve crossing to the A " potential energy surface correlating with the next lower rotational asymptote. (C) 1998 Elsevier Science B.V. All rights reserved.