Matrix and ab initio infrared spectra of thiourea and thiourea-d4

The FTIR spectrum of thiourea and thiourea-d(4) isolated in argon and nitrogen matrices are presented for the first time and discussed in terms of normal modes predicted by ab initio calculations, Vibrational frequencies, IR intensities and isotopic shifts obtained from the density functional B3-LYP/6-31+G(2d,p) calculations show the most satisfactory agreement with experiments. In contrast with previous results, the present theoretical study indicates non-planarity of the molecule. The lowest energy structure has C-2 symmetry and the less stable isomers has C-s symmetry. Experimental data clearly indicate the presence of a single isomer in the vapor. The decomposition of thiourea for vaporization temperature over 410 K is also discussed. (C) 1998 Elsevier Science B.V. All rights reserved.