Structural study of sulfamic acid at 4.2 K by ENDOR-detected NMR

The electron–nuclear double resonance method (ENDOR) is used to obtain greatly enhanced NMR signals from the distant deuterium nuclei of perdeuterated sulfamic acid (ND3SO3) in single crystals at 4.2 K. The structural information is obtained by measuring the quadrupole coupling tensors of the deuterium atoms and their direction cosines. There is very good agreement between the N–D bond angles derived from these ENDOR-detected NMR (EDNMR) results and bond angles from neutron diffraction data at 78 K. Relationships between the deuterium quadrupole constants and N–D and D⋅⋅⋅O bond lengths are derived and discussed.