POLARIZED INFRARED AND RAMAN-SPECTRA OF UREA PHOSPHORIC-ACID AND UREA ARSENIC ACID SINGLE-CRYSTALS

The polarized infrared and Raman spectra of single crystals of urea-phosphoric acid, (NH2)2CO . H3PO4, its deuterated analogue, (ND2)2CO . D3PO4, and urea-arsenic acid, (NH2),CO . H3AsO4, were measured. The results obtained are discussed on the basis of the crystal structure and the selection rules. Characteristic spectral features due to hydrogen bond vibrational modes were identified, from their polarization behaviour, as arising from the very short, almost symmetrical O ... H ... O hydrogen bond connecting the urea and phosphoric (or arsenic) acid molecules and from two other strong O - H...O hydrogen bonds, linking different adducts.