The fundamental building blocks of molecules that lead to the origin of life in the Universe can be formed on cosmic icy dust grains in the interstellar medium (ISM). For a quantitative understanding of the chemical evolution towards complex molecules, it is essential to know the behaviors of relatively small radical species on icy grains at low temperatures (e.g., 10 K). However, elementary processes such as radical adsorption, diffusion, and chemical reactions are difficult to characterize from experimental studies alone, whereby quantum chemistry play a key role. We have used a quantum mechanics/molecular mechanics (QM/MM) method to determine binding energies of the radical species on ices (e.g., OH, HCO, CH3O, CH3, …). A range of binding energies was observed for each radical, where the interaction energies between the radical and ice, in particular orbital interactions, electrostatic attractions, and strong Pauli repulsion control the strength of the binding energy. Also, we have combined laboratory experiments and quantum chemistry to understand how OH radical behaves on ice. Our experiments created OH radical on water ice by photodissociation of H2O at interstellar conditions. Computational studies rationalized the mechanisms for the OH radical photodesorption on ice and the proton hole transfer in ice. Our findings offer important mechanistic insights to understand radical process on interstellar ices.

Radical processes on interstellar ices: A combined experimental and quantum chemical study

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.