Vibrational predissociation of HFHCl by overtone excitation of HF

The high-resolution laser-induced-fluorescence spectrum of the ν = 3 excitation of the HF stretch in HFHCl is reported. The complex was formed in a supersonic jet of HF and HCl molecules expanded in argon. The HF submolecule was pumped from ν = 0 to ν = 3 by radiation from a Ti: sapphire ring laser operating in the (11–12) × 103 cm−1 range. Both Δν = 1 and ν = 2 emission of the HF fragment were observed by large-area PbS and Ge detectors, respectively. A single band with K″ = 0 and ΔK = 0 for both isotopic species, HFH35Cl and HFH37Cl, was observed. For HFH35Cl the band origin is ν0 = 11 309.122 (11) cm−1, and the rotational constant [Formula: see text]. A perturbation centered at J = 6 in the ν = 3 level is observed for HFH35Cl. The average linewidth of 300 MHz in this overtone region is approximately 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-dependence was detected.