Could HCN Be Responsible for the Formamide Synthesis in Earth’s Primitive Atmosphere?

Abstract

The forward and reverse H 2 O + HCN ↔ HCONH 2 global reactions were studied along temperatures from 200 to 4000 K. Equilibrium geometries and vibrational frequencies were obtained from calculations at the Coupled Cluster theory with single and double excitations (CCSD)/cc-pVDZ level; whereas enthalpies, Gibbs energies, and thermal rate constants were achieved by means of the CCSD(T)/CBS//CCSD/cc-pVDZ combined treatment. The estimates performed considering physical and chemical conditions proposed for the primitive atmosphere of Earth indicate that the formamide concentration might be 3.0–4.4 times larger than the one for HCN at 700 K, suggesting that this forward gas phase reaction could provide an efficient production route for formamide during an age just before the formation of early oceans. This route is also considerably fast once the chemical equilibrium is attained in some decades at this temperature. In short, our research reinforces that more complex organic compounds, such as formamide, could be synthetized in the Earth’s primordial atmosphere, even considering a neutral atmosphere scenario composed mainly by H 2 O, CO 2 , and some N 2 .