Rotational analysis of the perpendicular vibrational bands of <sup>32</sup>SF<sub>6</sub>-Ar and <sup>32</sup>SF<sub>6</sub>-<sup>34</sup>SF<sub>6 </sub>complexes at 10.6 μm

<sec>Sulfur hexafluoride (SF<sub>6</sub>) is widely used in the electrical and electronic industries. It is also an important green-house gas. The study of spectra and structures of weakly bound complexes containing SF<sub>6</sub> is helpful to gain a deep understanding of the intermolecular interactions between SF<sub>6</sub> and other atoms or molecules. The rotationally resolved spectrum of the perpendicular vibrational band of <sup>32</sup>SF<sub>6</sub>-Ar in the <sup>32</sup>SF<sub>6</sub> <i>v</i><sub>3</sub> band region has been reported previously but the rotational analysis was not completed. In this work, this vibrational band of <sup>32</sup>SF<sub>6</sub>-Ar is re-investigated. The jet-cooled rovibrational spectra of SF<sub>6</sub>/Ar/He gas mixtures are measured by a continuous-wave distributed feed-back quantum cascade laser (DFB-QCL) at 10.6 μm with a segmented- rapid-scan data acquisition scheme. The gas mixture (SF<sub>6</sub>∶Ar∶He = 0.12∶1∶100) is expanded into a cylinder vacuum chamber through a 0.8 mm pin-hole nozzle. The probe laser is reflected about 90 times by a pair of astigmatic mirrors inside the chamber. The observed spectrum is analyzed by the standard symmetric-top Hamiltonian with the program PGOPHER. When the resonance interaction between the <i>l</i> = <inline-formula><tex-math id="M1">\begin{document}$ \pm 1 $\end{document}</tex-math></inline-formula> levels in the double-degenerate excited vibrational state of <sup>32</sup>SF<sub>6</sub>-Ar is considered, which was ignored in previous studies, a successful rotational analysis of the perpendicular vibrational band is conducted. The band-origin of the perpendicular band is determined to be <i>v</i><sub>0</sub> = 947.45300(58) cm<sup>–1</sup> and the resonance interaction parameter is <i>q</i> = –0.002325(70) cm<sup>–1</sup>. A set of absorption lines close to the <i>Q</i> branch of the <sup>32</sup>SF<sub>6</sub> <i>v</i><sub>3</sub> band is tentatively assigned to the perpendicular vibrational band of <sup>32</sup>SF<sub>6</sub>-<sup>34</sup>SF<sub>6</sub> complex. This band is heavily overlapped by the monomer lines so that very few lines can be assigned. The band-origin of this band is estimated to be 948.1181(12) cm<sup>–1</sup>. These results will be useful for developing highly accurate intermolecular potential energy surfaces for SF<sub>6</sub>-Ar complex and SF<sub>6</sub> dimer in the future.</sec>