Kinetics of the NH3 and CO2 solid-state reaction at low temperature
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 and CO2 solid-state reaction in ice films, the product of which is ammonium carbamate (NH4+NH2COO−). It is a first-order reaction with respect to CO2, with a temperature-dependent rate constant fitted to the Arrhenius law in the temperature range 70 K to 90 K, with an activation energy of 5.1 ± 1.6 kJ mol−1 and a pre-exponential factor of 0.09−0.08+1.1 s−1. This work helps to determine the rate of removal of CO2 and NH3, via their conversion into ammonium carbamate, from atmospheric and interstellar ices. We also measure first-order desorption energies of 69.0 ± 0.2 kJ mol−1 and 76.1 ± 0.1 kJ mol−1, assuming a pre-exponential factor of 1013 s−1, for ammonium carbamate and carbamic acid, respectively.