First <i>Ab Initio</i> Line Lists for Triatomic Sulfur-Containing Molecules: S₂O and S₃

We present in this paper the first room temperature rovibrational line lists for the main isotopologues of disulfur monoxide (S₂O) and thiozone (S₃) variationally computed from newly developed <i>ab initio</i> potential energy and dipole moment surfaces (PESs and DMSs). S₂O and S₃ are supposed to be potential candidates for astronomical detection, especially in the Venusian atmosphere where sulfur chemistry plays a major role. Contrary to other stable sulfur-containing species like SO₂ or H₂S, there is much less experimental data for the short-lived reactive S₂O and S₃ molecules. Indeed, the infrared spectra of S₂O and S₃ are quite complicated to analyze without consistent theoretical predictions because they contain both high <i>J</i> (∼100) and a lot of hot band transitions, even at <i>T</i> = 296 K. In this work, we have constructed PESs based on the single-reference coupled cluster approach [CCSD(T)] and including corrections due to the scalar relativistic effects, DBOC, and highly excited Slater determinants. The structure of the excited electronic states of S₃ was also discussed. The nuclear-motion Eckart-Watson Hamiltonian expressed in terms of normal-mode irreducible tensor operators was used to compute the energy levels. For line intensity calculation, <i>ab initio</i> DMSs were computed at the CCSD(T)/aug-cc-pV5Z level of the theory. Rotation-vibration patterns in the fundamental bands of S₂O and S₃ have been simulated taking into account the recent Fourier-transform spectra of S₂O recorded at the SOLEIL synchrotron. The present work aims at providing line intensities of S₂O and S₃ that are missing in the literature as well as new spectroscopic support for atmospheric applications.