EXPERIMENTAL INSIGHT ON THE CONFORMATIONAL LANDSCAPE OF THE SF6 DIMER: EVIDENCE FOR THREE CONFORMERS

The rovibrational spectrum of both parallel and perpendicular bands of the chem{SF_6} dimer near the nub{3} band of chem{SF_6} monomer was reinvestigatedfootnote{R.-D. Urban and M. Takami, J. Chem. Phys. 103, 9132 (1995).} using high resolution jet-cooled infrared laser spectroscopy to provide deeper insight on its conformational landscape. Taking advantage of our versatile set-upfootnote{P. Asselin, Y. Berger, T. R. Huet, R. Motiyenko, L. Margulès, R. J. Hendricks, M. R. Tarbutt, S. Tokunaga, B. Darquié, PCCP 19, 4576 (2017).}, jet-cooled spectra were recorded by combining different geometries of supersonic expansions, chem{SF_6} concentrations seeded in a carrier gas and axial distances. Relaxation effects could be evidenced at very low rotational temperature leading to different conformational populations. Three spectral features (noted #1, #2 and #3) belonging to three dimer conformers are unambiguously identified on the grounds of 3 distinct S-S distances derived from the rovibrational analysis of parallel band contours in the 932-935 wn range. Symmetry assignment, a priori accessible from the perpendicular band structure of a spherical top dimer, could not be clearly proved. The dependence of such conformational infrared signatures as a function of expansion conditions provides additional information about population dependence and interconversion processes taking place between these three forms predicted to be nearly isoenergetic by theoretical calculationsfootnote{T. Vazhappilly, A. Marjolin and K. J. Jordan, J. Phys. Chem. B 120, 1788 (2016).}. Based on experimental considerations, a qualitative picture of the nearly flat potential energy surface of the chem{SF_6} dimer is proposed which could explain the dominant presence of #1 and #3 populations in fast/cold axisymmetric expansions and that of #1 and #2 populations in slow/hot planar ones._x000d_ _x000d