Controlling metal-surface reactions via vibrational excitation by plasmon-enhanced infrared near-fields

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K14584
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 32010:Fundamental physical chemistry-related
• Research Institution: The University of Tokyo
• Principal Investigator: Morichika Ikki 東京大学, 生産技術研究所, 助教 (60885391)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 振動回転励起 / 回転波束 / 赤外フェムト秒レーザー / プラズモニクス / 反応制御 / 表面科学

Outline of Final Research Achievements

A high-resolution pump-probe spectroscopy system using an intense mid-infrared femtosecond laser has been constructed for the rovibrational excitation of molecules in the gas and liquid phases. Through the strong interaction of the molecules with the intense pulsed electric field, multi-step excitation approaching a vibrational quantum number of 10 is demonstrated. For the gas-phase molecules, oscillations of the absorbance changes with respect to the pump-probe delay time are observed, which are found to result from rotational coherence generated by the pump irradiation using nonlinear response function theory. Moreover, to enhance interactions between molecules and mid-infrared pulses, we have designed and fabricated metallic nanostructures exhibiting plasmon resonance in the mid-infrared range. It has been demonstrated that the enhanced electric field associated with plasmon excitation enables efficient vibrational excitation of molecules on a metal surface.

Free Research Field

光量子科学

Academic Significance and Societal Importance of the Research Achievements

本研究課題では，高強度赤外パルス電場を作用させることで，CO2分子の振動量子数10に迫る多段階励起を達成した．この振動エネルギーは，金属触媒を利用したCO2還元反応の活性化障壁を十分に超えており，振動励起による反応制御実現の可能性を示す成果である．特に，高振動励起状態に回転コヒーレンスを生成した例は過去になく，赤外光により分子の振動・回転を同時に制御できることを実験的に示した点は学術的に意義がある．また，金属ナノ構造のプラズモン増強電場により，金属表面の分子を高効率に振動励起できることが本研究課題により明らかとなり，本手法を金属表面反応へ応用することで，高効率な反応制御法の実現が期待される.