INFRARED SPECTRA AND CRYSTALLINE PHASE TRANSITIONS OF AMMONIUM NITRATE

Abstract

The infrared spectra of solid crystalline films of ammonium nitrate were measured at temperatures ranging between the melting point (169 °C) and liquid air temperature (−190 °C). Four different spectra were obtained which are shown to belong to phase I, II, IV, and (very probably) VII. Phases III and V were not encountered; only transitions [Formula: see text], [Formula: see text], and [Formula: see text] were observed. A spectrum measured at −190 °C after rapid cooling is shown to correspond to a mixture of phases IV and VII. The symmetry properties of the different phases are discussed in relation with their infrared spectra.