Theoretical study of the stable C 2 and C s symmetry isomers of urea

Abstract

The energy surface of the urea molecule was studied at the Møller-Plesset, B-LYP and B3-LYP density functional levels. The scanning of the energy surface indicates the presence of two energy minima corresponding to non-planar C2 and Cs symmetry structures. The C2 symmetry structure is the most stable one, while the Cs symmetry isomer lies 6 kJ mol −1 above the lowest energy minimum. The infrared spectra of the C2 symmetry stable isomer were computed at the MP2/DZ(d,p), B-LYP/DZ(d,p), B-LYP/6-311+G(d,p) and B3-LYP/6-311++G(2d,p) levels and the assignment of the harmonic vibrational frequencies was accomplished through the calculated potential energy distribution of urea and urea-d4. The comparison between the MP2/DZ(d,p) and B-LYP/DZ(d,p) infrared spectra of the C2 and Cs symmetry isomers is presented and discussed.