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

Abstract

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 N₂H₆²⁺ and SO₄²⁻ ions show marked changes across the phase transitions. The torsional mode of N₂H₆²⁺ 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 SO₄²⁻ ion bands also show marked changes across the phase transitions, the v₁ and v₂ 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.