Infrared spectrum of deuterated betaine phosphite

Far-infrared spectra of deuterated betaine phosphite were investigated in the frequency range from 20 to 650 cm(-1) at temperatures between 10 and 300 K. Most of the observed polar phonon modes exhibit pronounced increase of damping on heating, to the ferroelectric phase transition at T-c2 = 298 K. The phonon at 568 cm(-1), which is responsible for anomalous spin-lattice relaxation observed in EPR experiment, shows anomalous increase of damping near T-c2. Anomalous damping of the mode near 250 cm(-1) is connected with the antiferrodistortive phase transition at T-c1 = 355 K. Soft relaxational mode is not resolved in our spectra because its frequency lies below our frequency limit. The comparison of our spectra with the spectra of protonated betaine phosphite revealed no frequency shifts of phonon modes. verifying the missing influence of deuteration on external vibration of betaine and phosphite groups.