Criegee intermediate-hydrogen sulfide chemistry at the air/water interface

We carry out Born–Oppenheimer molecular dynamic simulations to show that the reaction between the smallest Criegee intermediate, CH2OO, and hydrogen sulfide (H2S) at the air/water interface can be observed within few picoseconds.

. Radical distribution functions (in arbitrary unit) between H 2 S and H 2 O. Black and blue curves represent RDFs for H2S S··O H2O , H2S H··O H2O in the surface region, respectively.
The site-dependent interaction between H 2 S and water droplet is analyzed using the radial distribution function (RDF), as shown in Figure S2. The unit of RDF is arbitrary in the sense that it is a relative measurement of atom-site distribution versus the distance between two concerning atom sites. The RDF for H··Ow (H atom in H 2 S, and O atoms in water droplet) shows the formation of the hydration layer around the H atom. The radius of the first hydration layer is around 2.2 Å, indicating the hydrogen bond formation of H2S H··O H2O . The RDF for S··Ow (S atom in H 2 S, and O atoms in water droplet) shows the hydration layer with a larger radius (3.7 Å) being formed by the terminal S atoms in SO 2 , indicating weak interaction of H2S S··O H2O . Figure S3. (Left) Definition of θ 1 and θ 2 . Here, θ 1 is the angle between S … COM (center of mass of the water droplet) line and S … H1 line, where H1 is the H atom of H 2 S with shorter distance to the center of mass of the water droplet. θ 2 is the angle between the S … COM line and S … H2 line.

S3
H2 is the H atom of H 2 S with larger distance to the center of mass of the water droplet. (Right) The probability distributions P(θ 1 , θ 2 ) computed for H 2 S at the air-water interface.
The microstructure of orientation II is analysed in more detail. The angles of θ 1 and θ 2 as shown in the left panel of Figure S3 are defined to evaluate microscopic picture of orientation II, and their probability distribution is shown in the right panel of Figure S3. It can be seen that θ 1 is distributed over the angular region from 30° to 45°, while θ 2 is distributed over the angular region from 50° to 65°. This result indicates that only H1 atom in H 2 S tends to form hydrogen bond with water droplet. Figure S4. Radical distribution functions (in arbitrary unit) between CH 2 OO and H 2 O. Black, blue and red curves represent RDFs for CH2OO C··O H2O , CH2OO O1··O H2O , CH2OO O2··O H2O in the surface region, respectively.

S4
The site-dependent interaction between CH 2 OO and water droplet is analyzed using the radial distribution function (RDF), as shown in Figure S4. The RDF for O2··Ow (terminal O atom in CH 2 OO, and O atoms in water droplet) shows a hydration layer with a smaller radius and a higher peak than that of either O1··Ow (middle O atom in CH 2 OO, and O atoms in water droplet) or C··Ow (C atom in CH 2 OO, and O atoms in water droplet), indicating that the dominant interaction between CH 2 OO and water droplet stems from CH2OO O2··O H2O .