Vibrational study of phase transitions in (CH<inf>3</inf>) <inf>3</inf>NHNO<inf>3</inf>

(CH3)3 NHNO3 belongs to the monoclinic system with space group P 21/c (C2h5) with four molecules per unit cell. Raman and infrared spectra ( 10-5000 cm-1) of single crystals and polycrystalline samples of (CH3)3 NHNO 3 and of its N-deuterated derivative were investigated in the temperature range 90-415 K. Assignments of the measured frequencies to the internal vibrational modes were obtained. A systematic temperature dependent study of frequencies, bandwidths and integrated intensities was performed. The results indicate the existence of phase transitions at 359 and 407 K and both phase transitions show thermal hysteresis, characteristic of first order. In the high temperature phases II and I, the cations and anions achieve reorientational motion. © 1988 American Institute of Physics.