Molecular dynamics simulations predict an accelerated dissociation of H2CO3 at the air–water interface†
Abstract
The dissociation and decomposition reactions of carbonic acid (H2CO3) in bulk water have been thoroughly studied, but little is known about its reactivity at the air–water interface. Herein, we investigate the dissociation reaction of H2CO3 at the air–water interface using ab initio molecular dynamics and metadynamics. Our results indicate that H2CO3 (pKa = 3.45) dissociates faster at the water surface than in bulk water, in contrast to recent experiments and simulations which have shown that HNO3 (pKa = −1.3) has a lower propensity to dissociate at the water surface than in bulk water. We find that the water surface allows for a more structured solvation environment around H2CO3 than in bulk water, which contributes to a decrease in the dissociation energy barrier via a stabilization of the transition state relative to the undissociated acid. Given its decreased kinetic stability at the air–water interface, H2CO3 may play an important role in the acidification of atmospheric aerosols and water droplets.