Vibrational predissociation of an inert gas cluster containing an active molecule: The vHF=3 spectrum of Ar3HF

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The vHF=3←0 HF valence excitation spectrum of Ar3HF is obtained by intracavity laser induced fluorescence. The spectroscopic constants determined for the vHF=3 level are band origin ν0=11 310.4520(4) cm−1 (corresponding to the vibrational redshift of Δν=−62.355 cm−1), the rotational constants B=0.039 743(5) cm−1 and DJ=2.04(12)×10−7 cm−1. The changes in rotational constants upon HF valence excitation to v=3 are ΔB=1.08(5)×10−4 cm−1 and ΔC=1.01(6)×10−4 cm−1. The increase in C is interpreted as the occurrence of a 0.2% decrease in the Ar–Ar separation. Appreciable line broadening is observed in the Ar3HF (v=3) spectrum. Twenty-three lines in P and R branches are fitted by the Voigt profile with 60 (10) MHz Lorentzian component establishing the occurrence of significant vibrational predissociation for Ar3HF at vHF=3. This rate is consistent with the empirical scaling of the vibrational predissociation rate with the frequency redshift, observed for stronger hydrogen bonded complexes of HF. The scaling of the vibrational predissociation rate for ArnHF (n=1–3) with the argon number, n, is poorly defined.