Vibrational analysis of urea

Although a lot of work has been done on the vibrational analysis of urea, t here still remain some contradictions and uncertainties, mainly due to inte rpretation of the vibrational spectrum of crystalline urea based on force f ield calculations on isolated urea instead of on urea in its crystal phase. We have shown that this approach is not allowed in the case of urea. The v ibrational spectrum of urea was interpreted by measuring the solid state in frared spectra of eight isotopomers of urea at room temperature and at -196 degrees C, and Raman spectra at room temperature and at -120 degrees C, an d of a urea-water solution. Force field calculations from our recently publ ished article on isolated urea and on urea in its crystal structure, at the Hartree-Fock level with a 6-31++G** basis set, were also used. We have als o shown that high-pressure measurements using a "diamond anvil cell" are no t useful by performing a vibrational analysis.