Theoretical study for near-field induced photochemistry beyond the dipole approximation

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K05412
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 32010:Fundamental physical chemistry-related
• Research Institution: Hokkaido University
• Principal Investigator: Iwasa Takeshi 北海道大学, 理学研究院, 助教 (80596685)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 近接場光 / 双極子近似の破れ / 選択則

Outline of Final Research Achievements

In this study, we developed a theoretical method beyond the dipole approximation to elucidate the mechanism of photochemical reactions induced by localized near-field and clarified the difference between far-field and near-field excisions, as well as the selection rule for a photo-STM experiment. Furthermore, using a cluster model, we investigated the excited states of the supported molecules in consideration of the interaction between the metal substrate and the molecules, and found that the excited states of the supported molecules become broadly distributed according to the interaction with the metal, and that the higher excited states are dipole-allowed, but there are many dipole-forbidden states in the low energy region. Although the transition probabilities were also investigated using near-field light, but the reaction mechanism was not fully elucidated, and we intend to improve the metal model in the future.

Free Research Field

分子物理学

Academic Significance and Societal Importance of the Research Achievements

近接場光は伝搬光にはない局在性という特徴を持ち、回折限界と双極子近似を超えた局所的な分光・イメージングや光化学反応への展開が期待されている。実際、走査型プローブ顕微鏡と組み合わせた光STM実験で、単分子の分子内振動イメージングなどの原子レベルの分解能を持った分光や、単分子の光化学反応の誘起と解析も可能になってきている。近接場光と分子の相互作用から出てくる新しい科学を理解・開拓していくためには、実際の分子系において双極子近似を超えた選択則を議論できる理論化学に基づいた本手法が必要であり、今後も更に発展させていく。