Implications of the (H2O)n + CO ↔ trans-HCOOH + (H2O)n–1 (n = 1, 2, and 3) reactions for primordial atmospheres of Venus and Earth

Resumo The forward and backward (H2O)(n) + CO <-> HCOOH + (H2O)(n-1) (n = 1, 2, and 3) reactions were studied in order to furnish trustworthy thermochemical and kinetic data. Stationary point structures involved in these chemical processes were achieved at the B2PLYP/cc-pVTZ level so that the corresponding vibrational frequencies, zero-point energies, and thermal corrections were scaled to consider anharmonicity effects. A complete basis set extrapolation was also employed with the CCSD(T) method in order to improve electronic energy descriptions and providing therefore more accurate results for enthalpies, Gibbs energies, and rate constants. Forward and backward rate constants were encountered at the high-pressure limit between 200 and 4000 K. In turn, modified Arrhenius' equations were fitted from these rate constants (between 700 and 4000 K). Next, considering physical and chemical conditions that have supposedly prevailed on primitive atmospheres of Venus and Earth, our main results indicate that 85-88 per cent of all water forms on these atmospheres were monomers, whereas (H2O)(2) and (H2O)(3) complexes would represent 12-15 and similar to 0 per cent, respectively. Besides, we estimate that Earth's and Venus' primitive atmospheres could have been composed by similar to 0.001-0.003 per cent of HCOOH when their temperatures were around 1000-2000 K. Finally, the water loss process on Venus may have occurred by a mechanism that includes the formic acid as intermediate species. (AU)