The supersonic jet technique coupled to high resolution spectroscopy has proved for thirty years to be a valuable tool to unravel the structure and vibrational dynamics of weakly bound complexes at very low temperatures. In the present work, we report a rovibrational study of small van der Waals clusters containing sulfur hexafluoride using a tunable quantum cascade laser spectrometer coupled to a supersonic jet in the region of the SF6 v3 stretching vibration (947.9cm-1). Our experiments were able to produce a variety of complexes of SF6 either in a planar expansion with a slit nozzle or in an axisymmetric expansion with a pinhole nozzle, typically with a small percent of SF6 diluted in 6 – 8 bar of He. Firstly, rotationally resolved parallel and perpendicular bands of (SF6)2 were obtained, from which we were able to confirm the presence of a D2d conformer previously reported. In addition, two theoretically predicted but previously undetected conformers of (SF6)2 (C2h and C2) were observed. Secondly, we report the spectrum of (SF6)2-Rg heterotrimers (Rg = Ne, Ar, Kr, Xe) which display a remarkable linear dependence between the spectral shift (defined as the frequency difference between the band center of C2h or C2 conformer and the most intense (SF)2 -Rg band observed) and the polarizability of the Rg atom. Lastly, for the first time in gas phase, the fully resolved rotational spectra of SF6-Rg dimers have been observed in very low temperature conditions near the v3 band of the SF6 monomer, previously only seen in helium droplet experiments.

Jet-cooled high resolution infrared spectroscopy of small van der Waals SF6 clusters

253rd National Meeting (2017)

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