Infrared Spectra of Urea and Thiourea Thin Films on the Metal Surface

The infrared spectra of thin urea and thiourea films, several hundred Angstroms thick, on a steel plate were obtained using an optical system in which the beam polarized parallel to the plane of incidence was incident at 70° upon a steel plate covered with film. The spectra obtained showed that the c-axis of the urea crystal was parallel to the metal surface. However, the abnormal behavior of the NH2 bending and the NH2 twisting bands suggests that the urea molecule in the film was deformed from the planar structure. The intensities of the infrared bands of thiourea belonging to the B1 species decreased in the film, and it may be concluded that the c-axis of the crystal is nearly parallel to the metal surface. The considerable rise in frequency of the NH2 wagging band observed in the thin thiourea film may arise from the deformation of the crystal. As for the thioureacollodion film, thiourea A1 bands appeared to be very weak, corresponding to the C=S bond orientation parallel to the metal surface. The dic...