OH^• + HCl Reaction at the Surface of a Water Droplet: An Ab Initio Molecular Dynamical Study

Abstract

The Born–Oppenheimer molecular dynamics (BOMD) simulation has been performed to investigate the dynamics of the OH• + HCl reaction at the surface of a water droplet. The investigation suggests that the reaction occurred at the surface of the water droplet becomes almost 10 times faster than the corresponding gas-phase reaction. Besides, we have also performed the quantum mechanics/molecular mechanics calculation to calculate the unimolecular energy barrier of the reaction. The results indicate that the barrier height gets decreased by ∼0.3 kcal mol–1 at the surface of the water droplet, which also justifies the rate enhancement suggested by the BOMD simulation. The BOMD simulation also indicates that, at equilibrium, the product Cl• forms four hydrogen bonds with four interfacial water molecules, which stabilize the Cl• and resist it to escape from the surface.

Pre-deliquescent water uptake in deposited nanoparticles observed with in situ ambient pressure X-ray photoelectron spectroscopy

“…The surfaces of aerosol particles and droplets are distinct physical and chemical environments compared to their associated bulk phases. Reaction rates in micrometer-scale droplets have been measured (Jacobs et al, 2017;Marsh et al, 2019;Zhang et al, 2021) and modeled (Benjamin, 2019;Mallick and Kumar, 2020) to be higher than those in bulk water, with some reactions even proceeding spontaneously (Lee et al, 2019). For cloud and fog systems where the interfacial region makes up a significant fraction of the condensed aqueous phase, the reaction rate at the surface can be the rate-limiting step in multi-phase OH oxidation involving surface-active organic species such as pinonic acid (Huang et al, 2018).…”

Gas phase acidity of water clusters

“…The terminal hydrogen atom was found to be the key for most of the reactions involving water as a small cluster or as a droplet. 12,28–30 Therefore, first we have discussed the gas phase acidity of the terminal hydrogen for all the water clusters ((H 2 O) n , n = 1–20, 30, 35, 42, 54, 80, and 100). For clarity, we have marked these terminal hydrogen atoms with a red circle in Fig.…”

Nitrous acid (HONO) as a sink of the simplest Criegee intermediate in the atmosphere

“…1,6 The concentration of HONO in the Earth's atmosphere usually varies from 1.0 ppb to 9.7 ppb, [1][2][3]7 but in some areas, it can be as high as 20.0 ppb. 8 Although, the importance of HONO in tropospheric chemistry mainly comes from the fact that it produces OH by photo-dissociation, which is one of the most important oxidants present in the troposphere, [9][10][11][12][13] it is important to mention that HONO itself can also participate in various bimolecular reactions. 1 The bimolecular reactions of HONO with atmospheric co-reactants become more crucial in the nighttime as at night, due to the absence of photolysis, the concentration of HONO can become relatively high.…”