Electronic spectroscopy of toluene-rare-gas clusters: The external heavy atom effect and vibrational predissociationThe spectroscopy and predissociation dynamics of CN-Ne were investigated using a variety of laser excitation techniques. Properties of the A 2 ⌸ state ͑vibrational levels vϭ2, 3, and 4͒ were characterized through studies of the A -X system. Both spin-orbit components of CN(A) -Ne were subject to predissociation. The upper component (⍀ϭ1/2) was predissociated by rapid spin-orbit relaxation ͑Ϸ6 ps, no vibrational dependence͒. The lower component (⍀ϭ3/2) was predissociated by the nonadiabatic internal conversion process, CN(A 2 ⌸ 3/2 ,v) -Ne →CN(X 2 ⌺ ϩ ,vϩ4)ϩNe. Rates for predissociation by internal conversion were found to be exponentially dependent on the energy gap between the initial and final CN levels. These rates were relatively slow, permitting observation of rotationally resolved spectra for bands associated with the monomer ⍀ϭ3/2 vϭ3 and 4 levels. Double resonance techniques were 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 from spin-orbit and internal conversion predissociation were characterized. For the former, excess energy was channeled into rotational excitation of CN, and levels ofϪparity were preferentially populated. The excess energy in predissociation by internal conversion was released primarily to translational recoil. In the accompanying paper, Yang and Alexander present ab initio potential surfaces for CN-Ne. From these surfaces they predict ro-vibronic energies and predissociation rates for levels associated with A, vϭ3. Results that depended on the A state 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 the A and X states.