Rotational analysis of the (0,0) band of the B2Σ- X2Σ transition of ScS is reported. Spectrographic illustration of a hyperfine coupling transition in the ground state is demonstrated for the first time. This enables an order of magnitude to be obtained for γ″ (∼0.003 cm -1). The results for the other constants were: X state: B″ = 0.1971 cm -1, D″ = 5 × 10 -8cm -1, 4 b = 0.23 cm -1 (equal to that for ScO within the limits of measurement uncertainty); B state: B' = 0.1853 cm -1, D' = 6 × 10 -8cm -1, γ' = -0.0594 cm -1, which can be compared with pA2Π = 0.060 cm -1. It was found that the two excited states A2Π and B2Σ constitute an excellent example of pure precession ( ppp = 0.058 cm -1, and this enables the vibrational levels of A2Π to be numbered.