Theoretical and IR-matrix isolation studies on the urea and urea-D4,-13C, and-1,3-15N2 substituted molecules

Low-temperature Ar-matrix IR spectra of urea and urea-D-4, -C-13 and -1,3-N-15(2) substituted molecules were measured. The calculation accomplished at the Moller-Plesset (MP2)/aug-cc-pVTZ and at the density functional B3PW91/aug-cc-pVTZ levels provide contradictory results. The MP2/aug-cc-pVTZ calculations predict the C-2 symmetry urea conformer to be more stable than the C-S symmetry form, whereas, the B3PW91/aug-cc-pVTZ calculations predict oppositely. The Ar-matrix IR spectra show rather one than two urea conformers. The multiplet near 1400 cm(-1) is interpreted as manifestation of the V-as(CN2) mode Fermi resonance with a combination mode. (C) 2002 Elsevier Science B.V. All rights reserved.