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Solvation and Hydrolysis Reaction of Isocyanic Acid at the Air–Water Interface: A Computational Study
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posted on 2022-03-15, 19:08 authored by Jie Zhong, Liwen Li, Manoj Kumar, Xiao Cheng Zeng, Jun Zhang, Joseph S. FranciscoIsocyanic
acid (HNCO) is known to be inert to strong oxidants and
photolysis in the atmosphere but often appears in different forms
of smoke; therefore, it is linked to various smoke-related illnesses
due to tobacco usage or wildfire events. To date, the major loss pathway
of HNCO is believed to be through its uptake on aerosol droplets.
However, the molecular mechanisms
underlying such an uptake process are still incompletely understood.
Herein, we use the Born–Oppenheimer molecular dynamics (BOMD)
simulations to study solvation and hydrolysis reactions of HNCO on
water droplets at ambient temperature. The BOMD simulations indicate
that the scavenging of HNCO by water droplets is largely attributed
to the preferential adsorption of HNCO at the air–water interface,
rather than inside bulk water. Specifically, the H atom of HNCO interacts
with the O atom of interfacial water, leading to the formation of
a hydrogen bond (H-bond) of (HNCO)H···O(H2O), which prevents HNCO from evaporating. Moreover, the interfacial
water can act as H-bond acceptors/donors to promote the proton transfer
during the HNCO hydrolysis reaction. Compared to the gas phase, the
activation barrier is lowered from 45 to 14 kcal·mol–1 on the water surface, which facilitates the formation of the key
intermediate of NH2COOH. This intermediate eventually decomposes
into NH3 and CO2, consistent with the previous
study [Atmos. Chem. Phys. 2016, 16, 703−714]. The new molecular insight into HNCO solvation
and reaction on the water surface improves our understanding of the
uptake of HNCO on aerosols.
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still incompletely understoodrelated illnesses duenew molecular insightmolecular mechanisms underlyingmajor loss pathwayintermediate eventually decomposesinside bulk water3 sub2 subwater surface improvesbomd simulations indicatehnco hydrolysis reactionwater surfacekey intermediatewater dropletsinterfacial waterhydrolysis reactionshydrolysis reactionwildfire eventstobacco usagestrong oxidantsproton transferprevious studyprevents hncopreferential adsorptionoften appearslargely attributedisocyanic acidhnco interactsgas phasedifferent formsambient temperatureaerosol dropletsactivation barrier