Quantum chemical calculation on the potential energy surface of H 2CO 3 and its implication for martian chemistry

Abstract

A detailed theoretical study of the potential energy surface of H 2CO 3 is explored at the CCSD(T)//B3LYP/aug-cc-pVTZ level. On the potential energy surface, 12 isomers of H 2CO 3 are located. Their molecular properties such as geometries, vibrational frequencies, rotational constants, dipole moments, gas-phase acidities, and relative energies are calculated. Various reaction pathways and decomposition products have also been discussed. Among these products, CO 2 and H 2O are definitely the most favorable products with predominant abundance. Large energy barriers are predicted for other dissociation channels leading to the formation of oxygen, formaldehyde, and so on. These high energy channels are not important thermodynamically and kinetically, but they might occur in the presence of cosmic rays in astronomic environments. From the present work we suggest that chemical reactions between CO 2 and H 2O at the polar ice caps could be a potential source of H 2CO and O 2, in addition to the previously proposed mechanisms, i.e., the oxidation of methane and cosmic-ray-mediated production through the intermediate H 2CO 3. The results of the present work may provide useful data to improve our understanding of icy chemistry at the polar caps on Mars.