Distinguishing and identifying hydrogens in an NH3 group by I.R. spectroscopy

Combined low temperature isotopic dilution and polarized i.r. measurements have been performed on single crystal specimens of sulfamic acid, ⁺H₃NSO₃⁻, containing 5% D with respect to H. The three isotropically isolated νND bands observed in these spectra at 2302.5, 2313 and 2324 cm⁻¹ were polarized along different crystallograpkic axes, which allowed to assign them to specific hydrogen positions in the crystal and in the NH₃ groups. Comparison of neutron diffraction and vibrational frequency data shows that, despite the differences in NHO hydrogen angles, of all the geometric parameters the N⋯O distance only seems to correlate with the isolated N-D stretching frequencies.