First Ab Initio Line Lists for Triatomic Sulfur-Containing Molecules: S 2 O and S 3 .

We present in this paper the first room temperature rovibrational line lists for the main isotopologues of disulfur monoxide (S 2 O) and thiozone (S 3 ) variationally computed from newly developed ab initio potential energy and dipole moment surfaces (PESs and DMSs). S 2 O and S 3 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 SO 2 or H 2 S, there is much less experimental data for the short-lived reactive S 2 O and S 3 molecules. Indeed, the infrared spectra of S 2 O and S 3 are quite complicated to analyze without consistent theoretical predictions because they contain both high J (∼100) and a lot of hot band transitions, even at T = 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 S 3 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, ab initio DMSs were computed at the CCSD(T)/aug-cc-pV5Z level of the theory. Rotation-vibration patterns in the fundamental bands of S 2 O and S 3 have been simulated taking into account the recent Fourier-transform spectra of S 2 O recorded at the SOLEIL synchrotron. The present work aims at providing line intensities of S 2 O and S 3 that are missing in the literature as well as new spectroscopic support for atmospheric applications.