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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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Keywords:
- Methlypyrazine /
- photoelectron imaging /
- intersystem crossing /
- pump-probe /
- time-resolved spectroscopy
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图 1 (a)光电子影像装置实物图; (b)飞秒时间分辨光电子影像装置示意图[21]
Fig. 1. (a) Photoelectron imaging apparatus; (b) schematic diagram of the femtosecond time resolved photoelectron imaging setup.
图 2 (a)泵浦光323 nm, 探测光400 nm的各自单光和零时刻双光质谱;(b)泵浦光323 nm, 探测光400 nm作用下时间分辨母体离子信号, 图中实线表示拟合曲线, 圆圈代表实验数据
Fig. 2. (a) Two color (at time overlap) and one color mass spectra of 2-methlypyrazine at 323 nm pump and 400 nm probe; (b) time-resolved total ion signals of parent ion as a function of delay time between the pump pulse at 323 nm and the probe pulse at 400 nm. The circles are the experimental results, and solid lines are the fitting results.
图 3 泵浦光323 nm, 探测光400 nm, 在不同时间延迟下的光电子原始影像和BASEX变换后的影像(上排为原始影像, 而下排为BASEX变换后的影像.). 泵浦光和探测光都是线偏振光, 偏振方向为图平面竖直方向
Fig. 3. Time-resolved photoelectron raw images (shown in the upper row) and BASEX-inverted images (shown in the lower row) at various time delays observed at 323 nm pump and 400 nm probe.
图 4 (a)不同延迟时间下的光电子能谱; (b) 0 fs和92 ps时的光电子能谱
Fig. 4. (a) Photoelectron kinetic energy distributions (PKE) at different time delay; (b) photoelectron kinetic energy distributions at 0 and 92 ps.
图 5 六个峰强度随泵浦-探测时间变化图
Fig. 5. Time-resolved PKE bands intensity as a function of representative delay times.
图 6 (a) 0—4 ps泵浦-探测时间延迟下不同光电子峰强度变化; (b)不同光电子峰对应的不同泵浦-探测时间延迟下各向异性参数
Fig. 6. (a) The intensity changes of different photoelectronic peaks with 0–4 ps pump- probe time delay; (b) anisotropy parameters of the six rings as a function of pump-probe time delay.
图 7 (a) 105—130 ps泵浦-探测时间延迟下不同光电子峰强度变化; (b)不同光电子峰对应不同泵浦-探测时间延迟下的各向异性参数
Fig. 7. (a) The intensity changes of different photoelectronic peaks with 105–130 ps pump- probe time delay; (b) anisotropy parameters of the six rings as a function of pump-probe time delay.
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[1] De Gruijl F 1999 Eur. J. Cancer 35 2003
Google Scholar
[2] Ichihashi M, Ueda M, Budiyanto A, Bito T, Oka M, Fukunaga M, Tsuru K, Horikawa T 2003 Toxicology 189 21
Google Scholar
[3] Iqbal A, Stavros V G 2010 J. Phys. Chem. Lett. 1 2274
Google Scholar
[4] Domcke W, Stock G 1997 Adv. Chem. Phys. 100 1
[5] Gustavsson T, Improta R, Markovitsi D 2010 J. Phys. Chem. Lett. 1 2025
Google Scholar
[6] Schoenlein R W, Peteanu L A, Mathies R, Shank C V 1991 Science 254 412
Google Scholar
[7] Suzuki T, Wang L, Kohguchi H 1999 J. Chem. Phys. 111 4859
Google Scholar
[8] Song J K, Tsubouchi M, Suzuki T 2001 J. Chem. Phys. 115 8810
Google Scholar
[9] Ling F Z, Li S, Song X L, Wang Y M, Long J Y, Zhang B 2017 Sci. Rep. 7 15362
Google Scholar
[10] Toshinori S 2014 Bull. Chem. Soc. Jpn. 87 341
Google Scholar
[11] Farmanara P, Stert V, Radloff W, Hertel I V 2001 J. Phys. Chem. A 105 5613
Google Scholar
[12] Suzuki Y I, Horio T, Fuji T, Suzuki T 2011 J. Chem. Phys. 134 184313
Google Scholar
[13] Frad A, Lahmani F, Tramer A, Tric C 1974 J. Chem. Phys. 60 4419
Google Scholar
[14] Zhong D, Diau E W G, Bernhardt T M, Feyter S D, Roberts J D, Zewail A H 1998 Chem. Phys. Lett. 298 129
Google Scholar
[15] Wang L, Kohguchi H, Suzuki T 1999 Faraday Discuss. 113 37
Google Scholar
[16] Tsubouchi M, Whitaker B J, Wang L, Kohguchi H, Suzuki T 2001 Phys. Rev. Lett. 86 4500
Google Scholar
[17] 刘玉柱, 肖韶荣, 王俊锋, 何仲福, 邱学军, Gregor Knopp 2016 物理学报 65 113301
Google Scholar
Liu Y Z, Xiao S R, Wang J F, He Zhong F, Qiu X J, Knopp G 2016 Acta Phys. Sin. 65 113301
Google Scholar
[18] 刘玉柱, 陈云云, 郑改革, 金峰Gregor, Knopp 2016 物理学报 65 053302
Google Scholar
Liu Y Z, Chen Y Y, Zheng G G, Jin F, Knopp G 2016 Acta Phys. Sin. 65 053302
Google Scholar
[19] Liu Y Z, Knopp G, Qin C C, Gerber T 2015 Chem. Phys. 446 142
Google Scholar
[20] Fuji T, Suzuki Y I, Horio T, Suzuki T, Mitrić R, Werner U, Koutecký V B 2010 J. Chem. Phys. 133 234303
Google Scholar
[21] 凌丰姿 2018 博士学位论文(武汉: 中国科学院武汉物理与数学研究所)
Ling F Z 2018 Ph. D. Dissertation (Wuhan: Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences) (in Chinese)
[22] Hao Q L, Long J Y, Deng X L, Tang Y, Abulimiti B, Zhang B 2017 J. Phys. Chem. A 121 3858
Google Scholar
[23] Ling F, Li S, Wei J, Liu K, Wang Y M, Zhang B 2018 J. Chem. Phys. 148 144311
Google Scholar
[24] Dribinski V, Ossadtchi A, Mandelshtam V. A, Reisler H 2002 Rev. Sci. Instrum. 73 2634
Google Scholar
[25] Matsumoto Y, Kim S. K, Suzuki T 2003 J. Chem. Phys. 119 300
Google Scholar
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