Quantum chemical calculation on the potential energy surface of H2CO3 and its implication for martian chemistry

A detailed theoretical study of the potential energy surface of H2CO3 is explored at the CCSD(T)//B3LYP/aug-cc-pVTZ level. On the potential energy surface, 12 isomers of H2CO3 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, CO2 and H2O 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 CO2 and H2O at the polar ice caps could be a potential source of H2CO and O2, in addition to the previously proposed mechanisms, i.e., the oxidation of methane and cosmic-ray-mediated production through the intermediate H2CO3. The results of the present work may provide useful data to improve our understanding of icy chemistry at the polar caps on Mars.