INTERMOLECULAR VIBRATIONS AND SPIN-ORBIT PREDISSOCIATION DYNAMICS OF NEOH (X(2)PI)

Stimulated emission pumping of NeOH is used to access the bound intermolecular vibrational levels supported by the OH X (2) Pi(3/2) + Ne potential energy surface as well as predissociative levels correlating with the spin-orbit excited state of OH X (2) Pi(1/2) + Ne which lie more than 100 cm(-1) above the dissociation limit. Intermolecular stretching intervals and rotor constants yield the radial dependence of the average interaction between Ne and OH X (2) Pi(3/2,1/2), while the spacings between angular levels provide information on the anisotropy of the potentials. The lifetime of spin-orbit predissociative levels is found to increase by a factor of 3 upon intermolecular stretching excitation, from 8.5 ps to more than 27 ps. This increase in lifetime is attributed to the fall-off in the coupling between the two spin-orbit states with increasing intermolecular separation distance. The dominant coupling for spin-orbit predissociation is provided by the difference potential, the change in the intermolecular potential when the unpaired electron of OH lies in or out of the NeOH plane. The energies, rotor constants, and lifetimes of the bound and predissociative NeOH levels observed experimentally are compared with theoretical calculations of these quantities based on ab initio potentials for Ne + OH X (2) Pi by Yang and Alexander (accompanying paper). Remarkably good agreement is found between experiment and theory, given the weakness of the Ne + OH X (2) Pi interaction. (C) 1995 American Institute of Physics.