The influence of the environment in chemical reactivity: the HCOOH formation from the H2O + CO reaction.

Abstract

The reaction between carbon monoxide and water was studied occurring in an aerosol medium rich in methanol. This environment is plausible for the primitive and prebiotic Earth atmosphere. The chemical environment is expressed in terms of dielectric constant (ε) and the chemical system was modeled employing the polarizable continuum model (PCM). The main results were acquired from calculations employing the M06-2X density functional for the electronic structure calculations and the canonical variational theory with small curvature tunneling for the chemical kinetic calculations. The rise of ε affects both the thermochemistry and the kinetics of the reaction, increasing the barrier height and decreasing the rate constant for the reaction occurring at room temperature. For example, the rate constant at 300 K is 5-10× 10- 53 cm3 ⋅molecule- 1 ⋅s- 1 for low dielectric constant (ε < 3) and around 2-4× 10- 53 cm3 ⋅molecule- 1 ⋅s- 1 for ε between 7 and 40. Our results indicate that the ε variation allows a fine tuning to the rate of the reaction.