The microwave spectra of 79BrSCN and 81BrSCN have been measured and analysed to give rotational, centrifugal distortion, and Br quadrupole coupling constants. The molecule has been shown unambiguously to be BrSCN rather than BrNCS. A harmonic force field has been determined from combined vibrational and distortion data. With structural parameters for the SCN chain transferred from S (CN) 2, both effective and ground state average ...