Microwave spectroscopy was used to determine whether sulphonyl chloride isocyanate (SO₂CINCO) exists as a mixture of 71° and 110° isomers or as a single 94° isomer where the angle is the dihedral angle between the S-Cl bond and N = C bond, and whether the NCO group is linear or not. The microwave spectrum of SO₂CINCO was assigned for two isotopic species, SO₂³⁵CINCO and SO₂³⁷CINCO, by considering the Stark effect and the nuclear quadrupole splittings due to chlorine and nitrogen. Rotational constants and nuclear quadrupole coupling constants were determined from the assigned peaks. The bond angles and dihedral angles were derived from the six rotational constants of the two isotopes by imposing some constraints based on the electron diffraction study. The dihedral angle C = N-S-CI obtained in this study was 93.86 ± 0.04 ° and ∠NCO was 175.68 ± 0.02° . The results indicate that SO₂CINCO exists as the 94° form at the temperature (4° K) where the microwave spectrum was recorded and that the NCO group is not linear. / Ph. D.