2020 Fiscal Year Research-status Report
Multiscale modeling of radical diffusion and radical reactions on interstellar ices
| Project/Area Number |
19K03940
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| Research Institution | Hokkaido University |
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Principal Investigator |
Sameera W.M.C. 北海道大学, 低温科学研究所, 特任助教 (90791278)
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| Project Period (FY) |
2019-04-01 – 2022-03-31
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| Keywords | Interstellar medium / Radical species / QM/MM methods |
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| Outline of Annual Research Achievements |
The fundamental building blocks of molecules, which lead to the origin of life in the Universe, can be formed on cosmic icy dust grains in the cold 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 at encounter each other are still unknown and treat as a “black box” in the astrochemical models. To overcome this limitation, I use quantum chemistry to study the radical processes on ice.
During the 2020-2021 academic year, I studied the behavior of OH radical on ice. Once an OH radical on ices meets an electron, an OH anion can be formed. My quantum chemical calculations indicated that the OH anion could react with a water molecule on ice, which is a barrierless reaction. Then, the OH anion in ice can be transported to ice bulk through the proton hole transfer, giving rise to a negative current that we confirmed experimentally.
Also, I have studied the behavior of an CH3O radical on ice. A range of binding energies, 0.10-050 eV, was observed, where the electrostatic attraction, Pauli repulsion, and orbital interactions control the strength of the binding energy. Based on my data, I argue that a more realistic astrochemical model can be achieved by taking a distribution of binding energies instead of a single value.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
My calculations gave quantitative insights into the OH radical behavior on ices. The experimental research proved my theoretical predictions. Thus, progress of the current project has been very productive.
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| Strategy for Future Research Activity |
During the 2021-2022 academic year, I aim to study the behavior of SH radical on ice. Binding energies of SH radical on ices will be calculated. Ground and excited-state potential energy surfaces of SH-ice complexes will be computed to check whether SH radicals on ice desorb upon photoexcitation.
Also, I aim to study OH radical diffusion on ices. For this purpose, ground-state potential energy surfaces will be calculated using quantum chemical methods. Once the diffusion paths are determined, the stationary points, specifically local minima (LMs) and transition states (TSs), will be collected. From the relative energies of the selected stationary points (i.e., LMs or TSs), the reaction barrier of the lowest energy reaction path(s) will be calculated, and then the diffusion barrier will be determined.
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