Red-degraded bands observed in absorption in the region 3600â 3900 à when strontium sulphide is heated in a carbon tube furnace to about 2000°C are assigned to a ¹Î£⁺⠹Σ⁺ system of SrS. The lower state is probably the ground state : the upper state is strongly perturbed. Constants derived from the analysis of five bands are : [graphic ommitted] With µ(⁸⁸Sr³²S)= 23.452 a.m.u., r e(X ¹Î£⁺)= 2.4405 à . Ground-state properties of the diatomic oxides and sulphides of the group 2 metals are briefly compared.