Infrared Spectroscopic Study of Ammonia – Sulfur Dioxide – Water Solid State System

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Abstract
Products formed during the solid state reactions between ammonia and sulfur dioxide in the presence or absence of water have been investigated by infrared spectroscopy. Warming of a low-temperature matrix of SO2 with excess NH3 produces (NH3)2•SO2 at −90 °C. This adduct decomposes near −50 °C into NH3•SO2 which has a yellow color. With excess SO2 only NH3•SO2 appears at −150 °C. The 1:1 complex disappears from the low-temperature infrared window at about −20 °C. With H2O present in the matrix, (NH3)2•SO2 is converted at −80 °C into ammonium sulfite which is stable to room temperature where it can be pumped off readily from the infrared window. With less than the stoichiometric amount of water, the final product of the warming sequence is ammonium pyrosulfite whose infrared spectrum varies considerably with experimental conditions. The pyrosulfite reacts further with water to give ammonium bisulfite. The infrared spectra of solid ammonium bisulfite and perdeuteroammonium bisulfite show that the hydrogen in the bisulfite ion is bonded to the sulfur atom. Vibrational assignments have been made for all the compounds.

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