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中国物理学会期刊

2-甲基吡嗪分子激发态系间交叉过程的飞秒时间分辨光电子影像研究

CSTR: 32037.14.aps.69.20200092

Intersystem crossing of 2-Methlypyrazine studied by femtosecond photoelectron imaging

CSTR: 32037.14.aps.69.20200092
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  • 飞秒时间分辨光电子影像技术和飞秒时间分辨质谱技术相结合, 研究了2-甲基吡嗪分子电子激发态超快非绝热弛豫动力学. 用323 nm光作为泵浦光, 把2-甲基吡嗪分子激发到第一激发态S1, 用400 nm光探测激发态演化过程. 通过时间分辨质谱技术测得S1态的寿命为98 ps. 实验中, 实时观察到了单重态S1向三重态T1的系间交叉过程. 通过分析发现, 跟吡嗪分子S1态的动力学过程不同, 2-甲基吡嗪分子激发到S1态后, 不仅S1 → T1系间交叉过程是S1态主要衰减通道, S1 → S0内转换过程也是S1态另一个主要衰减通道. 发挥飞秒时间分辨光电子影像技术的优点, 实验上得到不同泵浦-探测时间延迟的光电子角分布, 从角分布信息结合光电子能谱信息, 尝试观察2-甲基吡嗪分子的非绝热无场准直, 但由于2-甲基吡嗪分子对称性比吡嗪分子更低, 对称性更低分子准直现象的观察更有挑战性, 在实验中未能观察到非绝热准直动力学. 本工作为2-甲基吡嗪分子S1态非绝热弛豫动力学提供了较清楚的物理图像.

     

    The ultrafast nonadibatic relaxation dynamics of the excited state of 2-methylpyrazine has been studied by using femtosecond time-resolved photoelectron imaging and femtosecond time-resolved mass spectrometry. The first excited state S1 of 2-methylpyrazine was excited by 323 nm pump light, and the excited state deactivation process is detected by 400 nm probe light. The lifetime of S1 state 98 ps is obtained by time-resolved mass spectroscopy. The intersystem crossing from the S1 state to the T1 state is observed on real time. The relaxation dynamics of S1 state of 2-methlypyrazine is different from that of pyrazine, the results show that the intersystem crossing process between S1 and T1 is the main relaxation channel of S1 state of 2-methlypyrazine, but the internal conversion process between S1 and S0 is also a main relaxation channel of S1 state. By using the advantages of femtosecond time-resolved photoelectron imaging, the photoelectron angular distribution at different pump-probe time delay was obtained experimentally. From the photoelectron angle distribution combined with photoelectron kinetic energy distributions, we tried to observe the field-free nonadiabatic alignment. However, due to the fact that the molecular symmetry of 2-methylpyrazine is lower than that of pyrazine, it is more challenging to observe the phenomenon of molecular nonadiabatic alignment with lower symmetry. Therefore, it is fail to observe nonadiabatic alignment feature of 2-methylpyrazine in this experiment. This work provides a clearer physical picture for S1 state nonadibatic relaxation dynamics of 2-methylpyrazine.

     

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