SPECTROSCOPY AND NONADIABATIC PREDISSOCIATION OF CN-NE

The spectroscopy and predissociation dynamics of CN-Ne were investigat ed using a variety of laser excitation techniques. Properties of the A (2) Pi state (vibrational levels upsilon = 2, 3, and 4) were characte rized through studies of the A-X system. Both spin-orbit components of CN(A)-Ne were subject to predissociation. The upper component (Omega = 1/2) was predissociated by rapid spin-orbit relaxation (tau approxim ate to 6 ps, no vibrational dependence). The lower component (Omega = 3/2) was predissociated by the nonadiabatic internal conversion proces s, CN(A (2) Pi(3/2), upsilon)-Ne --> CN(X (2) Sigma(+), upsilon + 4) Ne. Rates for predissociation by internal conversion were found to be exponentially dependent on the energy gap between the initial and fin al CN levels. These rates were relatively slow, permitting observation of rotationally resolved spectra for bands associated with the monome r Omega = 3/2 upsilon = 3 and 4 levels. Double resonance techniques we re used to simplify the spectra and establish ro-vibronic assignments. Details of the intermolecular potential-energy surfaces were derived from these data. CN final state population distributions resulting fro m spin-orbit and internal conversion predissociation were characterize d. For the former, excess energy was channeled into rotational excitat ion of CN, and levels of-parity were preferentially populated. The exc ess energy in predissociation by internal conversion was released prim arily to translational recoil. In the accompanying paper, Yang and Ale xander present ab initio potential surfaces for CN-Ne. From these surf aces they predict ro-vibronic energies and predissociation rates for l evels associated with A, upsilon = 3. Results that depended on the A s tate surface alone were found to be in good agreement with experiment. Comparison of the internal conversion predissociation rates indicates that the ab initio calculations underestimated the coupling between t he A and X states. (C) 1997 American Institute of Physics.