TEMPERATURE DEPENDENCE OF THE LIBRATIONAL MOTION OF O-H GROUP IN CRYSTALLINE ACETIC ACID

Abstract

The Librational motion of O-H or N-H groups in most organic compounds gives rise to a characteristic broad structureless band not only in the liquid and amorphous phases but also in crystalline solids. To our knowledge an acceptable interpretation for this breadth has not yet been proposed. We have studied the temperature dependence of the infrared spectrum of crystalline $CH_{3}COOH, CH_{3}COOD$ and $CD_{3}COOD$. For this substance the crystal geometry is accurately known from neutron diffraction studies. The O-H (O-D) librational motion shows a behavior with temperature $(\nu, I_{max}, \Delta \nu_{1/2})$ different from other internal modes. The spectra of mixed crystals of isotopic species have been also recorded and studied. They show unusual Spectral properties. Attempts at interpretation will be presented.