Sublimation and Infrared Spectral Properties of Ammonium Cyanide

The ammonium ion (NH4+) has been suggested to be present in interstellar ices and has been observed on the surfaces of planetary bodies using infrared (IR) spectroscopy as the primary means of identification. Evidence for several ammonium salts has also been found in the dust and surface ices of comet 67P/Churyumov-Gerasimenko. Here we present a laboratory study of ammonium cyanide (NH4CN) and report on several properties of this compound, measured with higher accuracy than in previous reports, including its IR band strengths and optical constants for use in quantifying its abundance in interstellar and planetary ices. We also report the first measurements since 1882 of NH4CN vapor pressures, sublimation fluxes, and sublimation enthalpy measured at temperatures relevant to subliming cometary ices (134–155 K). The density and refractive index of NH4CN at 125 K and the sublimation enthalpy and vapor pressures of NH3 at ~100 K are also reported.