Journal
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Volume 18, Issue 43, Pages 29756-29770Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c6cp06071d
Keywords
-
Funding
- Israel Science Foundation (ISF Grant) [172/12]
- US National Science Foundation (NSF Grant) [CHE 0909227, 1443140]
- AirUCI
- National Science Foundation [CHE-1152737]
- Academy of Finland [257479, 294752]
- Div Atmospheric & Geospace Sciences
- Directorate For Geosciences [1443140] Funding Source: National Science Foundation
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1152737] Funding Source: National Science Foundation
- Academy of Finland (AKA) [257479, 257479] Funding Source: Academy of Finland (AKA)
Ask authors/readers for more resources
Deprotonation of organic acids at aqueous surfaces has important implications in atmospheric chemistry and other disciplines, yet it is not well-characterized or understood. This article explores the interactions of formic acid (FA), including ionization, in collisions at the air-water interface. Ab initio molecular dynamics simulations with dispersion-corrected density functional theory were used. The 8-50 picosecond duration trajectories all resulted in the adsorption of FA within the interfacial region, with no scattering, absorption into the bulk or desorption into the vapor. Despite the known weak acidity of FA, spontaneous deprotonation of the acid was observed at the interface on a broad picosecond timescale, ranging from a few picoseconds typical for stronger acids to tens of picoseconds. Deprotonation occurred in 4% of the trajectories, and was followed by Grotthuss proton transfer through adjacent water molecules. Both sequential and ultrafast concerted proton transfer were observed. The formation of contact ion pairs and solvent-separated ion pairs, and finally the reformation of neutral FA, both trans and cis conformers, occurred in different stages of the dynamics. To better understand the deprotonation mechanisms at the interface compared with the process in bulk water, we used well-tempered metadynamics to obtain deprotonation free energy profiles. While in bulk water FA deprotonation has a free energy barrier of 14.8 kJ mol(-1), in fair agreement with the earlier work, the barrier at the interface is only 7.5 kJ mol(-1). Thus, at the air-water interface, FA may dissociate more rapidly than in the bulk. This finding can be rationalized with reference to the dissimilar aqueous solvation and hydrogen-bonding environments in the interface compared to those in bulk liquid water.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available