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 NH 3 and CO 2 solid-state reaction in ice films, the product of which is ammonium carbamate (NH 4 + NH 2 COO − ). It is a first-order reaction with respect to CO 2 , 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 CO 2 and NH 3 , 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 10 13 s −1 , for ammonium carbamate and carbamic acid, respectively. Ammonia and carbon dioxide play an important role in both atmospheric and interstellar ice chemistries.