VIBRATIONAL PREDISSOCIATION OF HFHCL BY OVERTONE EXCITATION OF HF

The high-resolution laser-induced-fluorescence spectrum of the upsilon = 3 excitation of the HF stretch in HFHCl is reported. The complex wa s formed in a supersonic jet of HF and HCl molecules expanded in argon . The HF submolecule was pumped from upsilon = 0 to upsilon = 3 by rad iation from a Ti:sapphire ring laser operating in the (11-12) x 10(3) cm(-1) range. Both Delta upsilon = 1 and Delta upsilon = 2 emission of the HF fragment were observed by large-area PbS and Ge detectors, res pectively. A single band with K'' = 0 and Delta K = 0 for both isotopi c species, (HFHCl)-Cl-35 and (HFHCl)-Cl-37, was observed. For (HFHCl)- Cl-35 the band origin is nu(o) = 11 309.122 (11) cm(-1), and the rotat ional constant ($) over bar B-3 = 0.1183 cm(-1). A perturbation center ed at J = 6 in the upsilon = 3 level is observed for (HFHCl)-Cl-35. Th e average linewidth of 300 MHz in this overtone region is approximatel y 10 times greater than that at the fundamental. The linewidths of the vibration-rotation transitions of HFHCl show considerable variations with both Cl isotope and J level. Although the isotopic dependence of the linewidths was observed in the fundamental, no perceptible J-depen dence was detected.