Abstract
Ammonia and carbon dioxide play an important role in both atmospheric and interstellar ice chemistries.This work presents a theoretical and experimental study of the kinetics of the low-temperature NH3 andCO2 solid-state reaction in ice films, the product of which is ammonium carbamate (NH4+NH2COO). Itis a first-order reaction with respect to CO2, with a temperature-dependent rate constant fitted to theArrhenius law in the temperature range 70 K to 90 K, with an activation energy of 5.1 1.6 kJ mol1 anda pre-exponential factor of 0.090.08+1.1 s1. This work helps to determine the rate of removal of CO2and NH3, via their conversion into ammonium carbamate, from atmospheric and interstellar ices. Wealso measure first-order desorption energies of 69.0 0.2 kJ mol1 and 76.1 0.1 kJ mol1, assuminga pre-exponential factor of 1013 s1, for ammonium carbamate and carbamic acid, respectively.