High-level ab initio study of disulfur monoxide: Ground state potential energy surface and band origins for six isotopic species

•16 ab initio PESs of S2O were constructed and validated.•The corrections beyond the CCSD(T) level of the theory were included and analyzed.•The coupled cluster energies were extrapolated to the full configuration interaction limit.•For the first time, the agreement within 0.5 cm−1 was achieved for all band origins which were experimentally studied by high-resolution.•The validity of the advanced ab initio methods for molecules with a relatively large number of electrons was demonstrated.•For the first time, band origins of 32S216O, 32S34S16O, 34S32S16O, 32S33S16O, 33S32S16O, and 32S218O were predicted up to 5000 cm−1.