An infrared and raman study of the phase transitions and the torsional barrier in hydrazonium sulfate, N2H6SO4

Infrared and Raman spectra of N2H6SO4 have been investigated through the phase transitions at 230 K (III-II) and 483 K (II-I) and assignments made to the various vibrational modes. The assignments have been confirmed by studies of the deuterated compound. The internal modes of both N2H6 2+ and SO4 2− ions show marked changes across the phase transitions. The torsional mode of N2H6 2+ with a fundamental frequency of 517 cm−1 in the room-temperature phase II, disappears in the high-temperature phase, I, accompanied by the appearance of the v q bending mode at 845 cm−1. The torsional barrier is estimated to be ≈32 kJ mol−1. The hydrazonium ion in the high-temperature phase is comparable to ethane. The SO4 2− ion bands also show marked changes across the phase transitions, the v 1 and v 2 bands disappearing in the high-temperature phase. In the low-temperature phase, III, both molecular ions are more distorted than in the room-temperature phase.