Halogenated organics are emitted into the atmosphere from a variety of sources of both natural and anthropogenic origin. Their uptake at the surface of aerosols can affect their reactivity, for example, in processes that take part in ozone destruction due to production of reactive chlorine, bromine, and iodine radicals. Classical molecular dynamics (MD) simulations are carried out to investigate the interaction of small halomethane molecules of atmospheric relevance with a crystalline ice surface. The following halomethanes were studied: CH3Cl, CH2Cl2, CHCl3, CH3Br, CH2Br2, and CHBr3. MD simulations provide an invaluable insight into the adsorption behavior of halomethanes species. The adsorption energy is increasing as the number of halogen atoms is increasing. Moreover, brominated methanes exhibit a stronger interaction with the ice than their chlorinated analogs. Implications for the atmospheric chemistry are discussed.

The chlorine/water interface is of crucial importance in the context of atmospheric chemistry. Modeling the structure and dynamics at this interface requires an accurate description of the interaction potential energy surfaces. We propose here an analytical intermolecular potential that reproduces the interaction between the Cl2 molecule and a water molecule. Our functional form is fitted to a set of high level ab initio data using the coupled-cluster single double (triple)/aug-cc-p-VTZ level of electronic structure theory for the Cl2 - H2O complex. The potential fitted to reproduce the three minima structures of 1:1 complex is validated by the comparison of ab initio results of Cl2 interacting with an increasing number of water molecules. Finally, the model potential is used to study the physisorption of Cl2 on a perfectly ordered hexagonal ice slab. The calculated adsorption energy, in the range 0.27 eV, shows a good agreement with previous experimental results.