Experimental characterization of the energetics of low-temperature surface reactions

Astrochemical reactions on the surfaces of dust grains, for instance, are thought to be responsible for the formation of complex organic molecules, which are of potential importance for the origin of life. In the situation where the chemical composition of dust surfaces is not precisely known, knowledge of the fundamental reaction properties gains significance. Here we describe an experimental technique that can be used to measure the energy released in reactions involving of a single pair of reactants. These data can be directly compared with the results of quantum chemical computations leading to unequivocal conclusions regarding the reaction pathways and the presence of energy barriers. It allows the prediction of the outcomes of astrochemical surface reactions with higher accuracy compared with that achieved based on gas-phase studies. However, for the highest accuracy, some understanding of the catalytic influence of specific surfaces on the reactions is required. The method was applied to study the reactions of C atoms with H2, O2 and C2H2. The formation of HCH, CO + O and triplet cyclic-C3H2 products has been revealed, correspondingly