Kinetics of the NH3 and CO2 solid-state reaction at low temperature
Résumé
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 mol1 and
a pre-exponential factor of 0.090.08
+1.1 s1. 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 mol1 and 76.1 0.1 kJ mol1, assuming
a pre-exponential factor of 1013 s1, for ammonium carbamate and carbamic acid, respectively.