Evidence of Surface Catalytic Effect on Cosmic Dust Grain Analogs: The Ammonia and Carbon Dioxide Surface Reaction

Abstract

Surface chemistry on cosmic dust grains plays an important role in the formation of molecules at low temperatures in the interstellar and circumstellar environments. For the first time, we experimentally put in evidence the catalytic role of dust surfaces using the thermal reaction CO2 + 2NH3 → NH4 + NH2COO -, which is also a proxy of radical-radical reactions. Nanometre-sized amorphous silicate and carbon grains produced in our laboratory were used as grain analogues.Surface catalysis on grains accelerates the kinetics of the reaction studied at a temperature of 80 K by a factor of up to 3 compared to the reaction occurring in the molecular solid. The evidence of the catalytic effect of grain surfaces opens a door for experiments and calculations on the surface formation of interstellar and circumstellar molecules on dust. Ammonium carbamate on the surface of grains or released intact into protostellar or protoplanetary disk phases can give start to a network of prebiotic reactions. Therefore, there should be a great interest to search for ammonium carbamate and its daughter molecule, carbamic acid, in interstellar clouds, protostellar envelopes, and protoplanetary disks.

Ammonium salts are a reservoir of nitrogen on a cometary nucleus and possibly on some asteroids

“…To our knowledge, the production of ammonium salts via a gas phase reaction under astrophysical conditions has never been reported in the literature. Solid-state reactions appear more likely, because proton transfer or nucleophilic addition are highly facilitated by a dust surface and a solvent such as ice (30,31).…”

Neural-network assisted study of nitrogen atom dynamics on amorphous solid water – I. adsorption and desorption

“…The formation of the simplest molecule, H 2 , can be exclusively explained considering surface processes (Cuppen et al 2017). However, surface chemistry in space is not limited to the archetypal H 2 formation and the amount of possible chemical paths in surfaces increases constantly, determined both experimentally (Kobayashi et al 2017;Fedoseev et al 2017;Qasim et al 2019;Potapov et al 2019;Oba et al 2019;Potapov et al 2020) and theoretically (Enrique-Romero et al 2016;Meisner et al 2017;Rimola et al 2018;Molpeceres et al 2019;Lamberts et al 2019). The composition of solid bodies (known as dust grains) in the interstellar medium depends on the temperature conditions of each particular astronomical object and the nature of the parent star.…”

Chemical dynamics in interstellar ice

“…Laboratory studies (Bossa et al 2009, Noble et al 2014, Potapov et al 2019 of the reaction enable to experimentally measure the partial orders α and β, the pre-exponential factor k 0 and the E a activation energy of the reaction. Note i. that the pre-exponential factor k 0 is not equal to 10 12 s −1 if the reaction is not an elementary process, several elementary steps being hidden in k 0 (Noble et al 2014), and ii.…”

“…Note i. that the pre-exponential factor k 0 is not equal to 10 12 s −1 if the reaction is not an elementary process, several elementary steps being hidden in k 0 (Noble et al 2014), and ii. the rate constant value can depend on the surface (Potapov et al 2019). Kinetic parameters have been measured in laboratory for several reactions (Theulé et al 2013).…”

“…As a consequence, the dynamics of the reactions is as important as the network of the reactions to determine the abundances of the formed iCOMs. The dynamics of solid-state chemistry is important to increase the molecular complexity since grains offer a place where molecules can meet and react, act as a third body that can evacuate the excess energy released by exothermic reactions, and sometimes plays a catalytic role by potentially lowering the activation energies of reactions (Potapov et al 2019).…”