Internal modes and normal coordinate analysis of sulphamic acid

Abstract Reinvestigation of the polarized Raman spectra of a single crystal of sulphamic acid in the internal mode region reveals Fermi resonance around 680 and 1060 cm −1 The N-H stretching mode exhibits a large shift of 280 cm −1 indicating medium strength hydrogen bonding in the crystal. The internal modes have been assigned on the basis of free molecular symmetry and verified by calculating the potential energy distribution. UBFF force constants have been refined using an IBM 370 computer. The results confirm a strengthening of the hydrogen bonding and a weakening of the N-S bond in sulphamic acid relative to its salts, e.g. potassium sulphamate.