High-resolution infrared spectra of the Ar–SO2 complex in the ν3 region of SO2: A global analysis of rovibrational spectra

In this work, infrared spectra and intermolecular potential energy surface of the Ar–SO₂ van der Waals complex are investigated experimentally and theoretically, respectively. Firstly, the infrared spectrum of the Ar–SO₂ complex in the ν₃ asymmetric stretching region of SO₂ is recorded using an external-cavity quantum cascade laser spectrometer in a supersonic slit jet expansion, and a total of 429 transitions are observed and assigned. A global analysis of these newly observed transitions, together with previously reported spectroscopic data of the microwave and SO₂ monomer v₁ excited state, is carried out using a Watson A-reduced asymmetric rotor Hamiltonian. The band origins of the spectra are accurately determined to be 1361.33300(21) and 1361.30097(18) cm^–1 for the two tunneling components, respectively. These values represent a blue shift of approximately 0.7 cm^–1 compared to the vibrational frequency of the SO₂ monomer ν₃ band. The tunneling splitting of Ar–SO₂ in the SO₂ monomer v₃ excited state is determined to be 960.0 (58) MHz, which is 22.3 and 103.4 MHz lower than that observed in the ground vibrational state and in the SO₂ monomer v₁ excited state, respectively. Furthermore, a three-dimensional intermolecular potential energy surface is constructed at the CCSD(T)/aug-cc-pVTZ level supplemented with bond functions, and the global minimum is determined to be a non-planar C_s geometry with structural parameters R = 3.59 Å, θ = 102.0°, and φ = 90.0°, respectively. What is more, the sign of the quartic centrifugal distortion constant D_K is found to strongly depend on transitions with different K_a quantum numbers, and this conclusion is supported by the good agreement between experimental observations and theoretical calculations.