Molecular interactions at interstellar surfaces

The study of interactions of atoms, radicals and molecules with dust particles is critical to understanding the balance between gas phase and solid-state material in the interstellar and circumstellar medium. These detailed interactions will determine the compositions of ice mantles on dust grains and, consequently, the chemistry that occur at the grain surfaces. We have recently calculated the interactions of molecules, such as CH₄, C2H6, CH2O, CH3OH, N2, NH₃, and H₂S, with models of amorphous solid water (ASW) surfaces using modern polarizable molecular force fields originally designed for the study of biomolecular systems in water. Calculated binding energies show quite favorable agreement with available experimental results. This methodology has great potential as an alternative to the more computationally demanding approach of using density functional theory (DFT). In addition, the force-field calculations do not suffer from the somewhat uncertain accuracy of DFT methods for weak interactions between molecules. This also allows for the study of layered ices and other multi-component ices.