VIBRATIONAL STUDY OF THE STRUCTURE AND POLARONS IN PIPERAZINE HEXAHYDRATE

The Raman spectrum of piperazine hexahydrate was observed over the who le wavenumber region at various temperatures (300-29 K). The spitting between the N-H stretch and the polaron was found to be 21 cm(-1) at 4 4 K. The bands due to the axial configuration of piperazine were above 200 K in both the H and D systems. The enthalpy difference in the equ atorial-axial equilibrium was calculated to be 8.1 and 7.6 kJ mol(-1) in the H and D systems, respectively. The phase transition was found a t ca. 170 K, and is ascribed to the order-disorder type associated wit h the axial configuration. The polaron was discussed group theoretical ly and reinvestigated on the basis of the coupling of the N-X stretch with optical lattice modes. It is noted that the polaron is little aff ected by the phase transition at 170 K or disorder in hydrogen positio ns.