超高速電子微分法で探査されたブロモフォームのUV誘導反応経路
Lars Hoffmann1,2, Benjamin W Toulson1, Jie Yang3
1Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
Journal of the American Chemical Society
|October 7, 2024
まとめ
超高速電子 difraktionは,紫外線光は,主に C-Br 結合を壊すのではなく,ブロモフォーム (CHBr3) をイソメリ化する. このイソメリゼーション経路は,イソ-CHBr3を形成し,迅速に発生し,直接解離と競合する.
科学分野:
- 化学物理学
- 写真化学
- 反応ダイナミクス
背景:
- 反応速度と製品分布を予測することは,特に超高速技術を必要とする短命の中間物質には困難です.
- ブロモフォーム (CHBr3) の紫外線光化学はよく研究されているが,直接のC-Br結合分裂に対するイソメリゼーションのような経路はまだ議論されている.
研究 の 目的:
- 超高速の方法を用いて紫外線刺激後のブロモフォームの構造的動態を直接観察する.
- 競合する反応チャネル,特にイソメリゼーションと直接解離,およびそれらのそれぞれの貢献を解明する.
主な方法:
- ガス相超高速メガエレクトロンボルト電子微分法 (MeV-UED) が採用された.
- 光反応を開始するために,単一の267nm光子の刺激が使用されました.
- 構造変化の追跡を可能にする5秒間の時間解像度.
主要な成果:
- 直接のC-Br結合破裂は200フェムト秒 (fs) 内に発生する.
- イソ- CHBr3 (Br- CH- Br- Br) へのイソメリゼーションは,同じ時間スケールで観察され,寿命は1.1ピコ秒 (ps) を超えた.
- 分岐比はイソメリゼーションを好む (約. 60%) を直接解離する.
結論:
- イソメリゼーションは,ブロモフォームUV光化学における重要な初期段階である.
- 観察された同位体形成と寿命は,ローミング反応機構を支持する.
- 初期分子ダイナミクスシミュレーションと一致する.
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