VIBRATIONAL OVERTONE (3-0) SPECTROSCOPY of $Ar_{2}HF$ AND $Ar_{3}HF$

Abstract

We report laser induced fluorescence spectra for the species $Ar_{2}HF$ and $Ar_{3}HF$. Three bands have been assigned to $Ar_{2}HF$. A b-type transition band, centered at $11323.80 cm^{-1}$ ($49 cm^{-1}$ red shift) is observed with rotational constants of the upper state A=0.11957, B=0.05855 and C=$0.03896 cm^{-1}$. This band is consistent with the pure v=3 HF stretch of the trimer. A second tenfold weaker a-type band with origin at $11387.86 cm^{-1}$ is assigned to the in-plane bending combination. A third, even weaker, band with c-type rotational structure is observed with origin at $11426.3 cm^{-1}$ and is assigned to the out-of-plane bending combination. The in-plane and the out-of-plane bending frequency are $64 cm^{-1}$ and $103.5 cm^{-1}$ respectively. These vibrations show a quite different dependence upon the HF vibrational state. The pure v=3 HF stretch of the tetramer $Ar_{3}HF$ is observed as a parallel band of a symmetric top. The band origin is $11310.45 cm^{-1}$($62 cm^{-1}$ red shift); the upper state rotational constant B=$0.03975 cm^{-1}$. All of the spectra lines shows a Doppler shape, with no evidence for vibrational predissociation. The with of the lines of all of the species $Ar_{n}HF$, n=0.3, are well fitted by a single temperature.