Rovibrational spectra of Ar–SO2 and (SO2)2 van der Waals complexes in the v1 region of SO2

Abstract

Rovibrational absorption spectra of Ar–SO2 and (SO2)2 van der Waals complexes generated in a slit supersonic jet expansion have been recorded in the v1 symmetric stretching region of SO2 monomer using an external-cavity quantum cascade laser. Two vibrational bands for (SO2)2 and one for Ar–SO2 are assigned and analyzed. All these vibrational bands are of a/c hybrid type. The observed infrared transitions are fitted together with previous radio frequency and microwave spectra, yielding precise molecular constants in both the ground and excited vibrational states for these two complexes. The band origins of (SO2)2 are determined to be 1150.30319(13) cm−1 for vibration on the electron-donor side and 1153.40911(10) cm−1 for vibration on the electron-acceptor side, which is shifted from that of the SO2v1 band by about −1.41 cm-1 and + 1.70 cm−1, respectively. The vibrational energies of the two tunneling components of Ar–SO2 are determined to be 1151.61315(11) cm−1 and 1151.64840(11) cm−1. The tunneling splitting of Ar–SO2 increases from 982.881(32) MHz in the ground state to 1056.7(34) MHz in the excited vibrational state, indicating a decrease of the tunneling barrier upon excitation of the SO2 symmetric stretching vibration.