Comparison of direct and resonant scattering for H-2+CN(A (2)Pi): Collisional energy transfer versus predissociation of CN(A)-H-2 complexes

Electronic predissociation of CN(A (2)Pi)-H-2 was examined by characterizin g action spectra and product state distributions. Both spin-orbit [CN(A (2) Pi(1/2))-H-2--> CN(A (2)Pi(3/2))+H-2] and internal conversion [CN(A (2)Pi(3 /2))-H-2--> CN(X (2)Sigma)+H-2] decay channels were observed. For compariso n with the predissociation data, CN(A)+H-2 collisional energy transfer was examined at temperatures near 10 K. The product state distributions resulti ng from collisions showed symmetry preferences that were not evident in the distributions resulting from predissociation. It is argued that the lack o f symmetry preferences in the predissociation dynamics is indicative of a r esonant scattering process. Qualitative differences in the predissociation and collisional transfer dynamics can be explained by considering the symme try properties of the intermolecular potential energy surfaces, and the reg ions of these surfaces that are sampled by each type of event. Most prediss ociation data was recorded for ortho CN(A)-H-2(J=1) complexes. A new spectr al feature of the complex, tentatively assigned to para CN(A)-H-2(J=0), was observed in this study. The predissociation dynamics of this state were si gnificantly different from those of the ortho complex. (C) 2000 American In stitute of Physics. [S0021-9606(00)00817-5].