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Laboratory of Molecular Reaction Stereodynamics

Group

Our group is affiliated with Department of Chemical Physics, University of Science and Technology of China at Hefei. We continuously have limited openings for graduate students and undergraduates. Doctoral researchers with knowledges and skills in atom / molecule / ion / electron impacts or ultrafast lasers are particularly welcome to join us as Post-Doctor or Research Associate.

Current Members

Shan Xi TIAN (Professor, sxtian@ustc.edu.cn)

Jie HU (Associate Professor, jiehu@ustc.edu.cn)

Guoqiang TANG (Doctor, Visiting Scholar)

  • Ziyuan LI (D5,liziyuan@mail.ustc.edu.cn)
  • Jingchen XIE(D4,xjc1997@mail.ustc.edu.cn)
  • Yaya ZHI (D3,zyy1997@mail.ustc.edu.cn)
  • Mengyuan FAN (D3,fanmy@mail.ustc.edu.cn)
  • Qiang GUO (D2,guoq20@mail.ustc.edu.cn)
  • Tiantian TONG (D2,tongtt@mail.ustc.edu.cn)
  • Mengqi ZHENG (D1, mqzheng@mail.ustc.edu.cn)
  • Yue WANG (M3, wy1989@mail.ustc.edu.cn)
  • Ye LIU (M2, liuye3457@mail.ustc.edu.cn)
  • Chenyi ZHANG(M2, zhangchenyi@mail.ustc.edu.cn)
  • Jiayi LIU (M1, jiayiliu@mail.ustc.edu.cn)
  • Alumni Since 2010

  • 2023: Ziwei Chen (PhD); Zixin Chen (MS)
  • 2022: Minfu Zhao (Visiting Scholar, 2021-2022); Caixiu Zhang (MS)
  • 2021: Xiao-Fei Gao (PD, 2020-2021); Bin Wu (PD, 2020-2021); Jie Hu (PD, 2018-2021)
  • 2020: Xiao-Fei Gao (PhD); Chun-Xiao Wu (PhD); Xin Meng (MS); Miao-Miao He (MS)
  • 2019: Hao Li (PhD)
  • 2018: Xu-Dong Wang (PhD, Top-level CAS president awardee); Jie Hu (PhD); Ling-Ling Chen (MS); Jin-Chen Xie (BS)
  • 2017: Yu-Feng Ye (MS); Zi-Yuan Li(BS)
  • 2016: Wen-Ling Feng (PhD); Meng-Yang Li (MS)
  • 2015: Chuan-Jin Xuan (MS)
  • 2014: Cen-Feng Fu (PhD); Tao Jin (BS); Qi Yu (BS); Xuejun Gong (BS)
  • 2013: Lei Xia (PhD, CAS president awardee), Zhou Zhang (MS), Xian-Jin Zeng (MS), Hong-Kai Li (MS), Meng-Yang Li (BS), Yifan Liu (BS)
  • 2012: Bin Wu (PhD); Yong-Feng Wang (PhD); Yun-Feng Xu (PhD); Fan Zhang (BS); Wen-Hao Liu (BS)
  • 2011: Liuli Chen (PhD); Sheng-Xi Jin (BS); Yu-Feng Ye (BS)
  • 2010: Hai-Bei Li (PhD); Qiang Feng (MS); Xiang-Ling Meng (BS); Jia-Xing Lin (BS), Xian-Jin Zeng (BS), Fan Zheng (BS)
  • Recent News

    Jan. 2024

    DEA of Cluster (CO2)n

    Fan, Xie, et al., JCP

    Clusters of molecular CO2 mimic the icy particles in the Martian and Venusian atmospheres or the icy shell of interstellar dust. An experiment-theory combinational study reveals novel dynamics about the competition formations of (CO2)m- and (CO2)m-1O- in the dissociative electron attachments of these clusters, which is accepted for publication on JCP.

    Dec. 2023

    Origin of Atmospheric O2

    Zhi, et al., Comm. Chem.

    Existence of molecular oxygen in the prebiotic atmosphere of earth (4*109 years ago) and the current Martian and Venusian atmospheres is important, but it is unclear about the origin of O2. Besides the reaction presented in textbooks, we found that dissociative electron attachment was another channel (Nature Chemistry 2016). Now, the collision with helium ion in solar winds is proposed as a noticeable pathway. This work is accepted for publication on Comm. Chem.

    Aug. 2023

    18' NCCD

    Poster Prize

    All members attended the 18th National Conference of Chemical Dynamics at Dalian (Aug. 17-20). Yaya Zhi got the second prize for his poster presentation. Congratulation!

    May 2023

    Anionic Carbon-Monoxide in Dark States

    Xie, et al., JCP (communication)

    Dissociative electron attachments to the metastable CO a3Π were found to undergo the dark quartet states of anion. This work is now accepted for publication on J. Chem. Phys. as Communication. However, such a spin-state selection is still puzzling.

    Oct. 2022

    Electron Impact with Liquid Surface

    Chen, et al., Acc. Chem. Res.

    A review of our recent studies of the electron impacts with the liquid-vapor interfaces of alcohols is accepted for publication on Accounts of Chemical Research. We also appreciate the contributions (theoretical simulations) of the collaborators (C.-F. Fu and J. Yang). More exciting results will be obtained by using our innovation 'time-delayed mass spectrometry' .

    Aug. 2022

    NCCD2022

    Poster Prize

    Our group attended National Conference of Chemical Dynamics (NCCD) at Huangshan City, Aug. 23-27, 2022. Ziyuan Li won the poster prize! The poster title was 'Electron-Induced Synthesis of Dimethyl Ether in the Liquid–Vapor Interface of Methanol'.

    Research

    Basic features of chemical reaction are inter-/intra-molecular energy and charge redistributions and molecular reconstructions. Electron- or charge-transfer process is a doorway of chemical reactions in plasma, flame, interstellar space, and solutions. Besides the developments of some unique and state-of-the-art experimental techniques, we are interested in the following three topics about electron-driven chemical reactions in gas- and liquid-phases.

    Dissociative Electron Attachment

    since 2012

    Dissociative electron attachment (DEA), e- + AB -> A + B-, is an important process of radiation damage and substance evolutions in interstellar space and planet atmospheres. From the point of fundamental view, DEA is a key step of electron-induced chemical reactions. Now the delay-line-detector (DLD) is utilized, which enables us to record the three-dimensional Newton sphere of the product ions under ion velocity map imaging (VMI) condition. The attaching electrons are monochromatized (energetically selected) with a trochoidal electron monochromator. Therefore, a high-resolution VMI experiment for the DEA dynamics can be done with this unique apparatus.

    We further supplement a spectrometer to record the electron-impact photoemissions (see J. Chem. Phys. 2020, 153, 024301 and the following picture). The pump-probe technique will also be introduced into this apparatus.

    Ion-Molecule Reaction

    since 2017

    Ion-molecule reaction is another important process in interstellar space and planet atmospheres. Recently, we set up a VMI apparatus to investigate the cation-molecule reaction dynamics. The working frequency is 10 KHz by using the DLD and our home-made pulsed ion source. This experimental improvement greatly facilitates the stereodynamics studies of charge and energy transfer.

    Liquid & Surface

    since 2018

    To study the electron-induced reactions in liquid and interface (consisting of the outermost layer and subsurface), we established a conceptually new method 'time-delayed mass spectrometry'.

    A tandem mass spectrometer was further developed by supplementing a quadrupole mass filter. Owing to this development, molecular orientations both on the outermost layer and in the subsurface are revealed; more importantly, in situ existence of molecular clusters and electron-induced synthesis in the liquid surface are confirmed for the first time. This powerful technique is promising to control the chemical reactions in the liquid-vapor interface.

    As shown in the following figure, electron (or ion, ultraviolet photon) will be utilized for pumping, and the the products could be desorbed from the liquid surface with infrared picosecond laser pulses. This new pump-probe technique will be used for studies of chemical dynamics on the liquid surface.

    Time-Resolved Transmission Electron Microscopy

    since 2020

    This project includes the development of ultrafast and coherent electron pulsed (picoseconds to femtoseconds) beam based upon a transmission electron microscope (TEM) and applications for the dynamics studies of structural (phase) transitions and chemical reactions in condensed (liquid) phase.

    Publication (since 2012)

    (†: contributed equally; * corresponding author)

    Guo, Q.; Zhi, Y.; Hu, J.*; Tian, S. X.* Steoreodynamics of the reactive collisions between carbon dioxide and helium ion. (Submitted)

    Chen, Z.; Li, Z.; Xie, J.; Zhang, P.*; Tong, T.; Wang, Y.; Hu, J.; Wörner, H. J.; Tian, S. X.* Direct observation of anionic yields from the liquid-vapor interface by electron irradiation. (Submitted)

    Fan, M.†; Xie, J.†; Wang, E.; Tian, S. X.* Evaporative cooling and reaction of carbon-dioxide clusters by low-energy electron attachment. Journal of Chemical Physics in press

    Chen, Z.; Li, Z.; Tian, S. X.* Anionic clusters produced in the low-energy electron irradiation of methanol liquid. Chinese Journal of Chemical Physics in press

    Zhi, Y.; Guo, Q.; Xie, J.; Hu, J.*; Tian, S. X.* Direct production of molecular oxygen from carbon dioxide and helium ion collisions. Communications Chemistry 2023, 6: 267. (open access, https://www.nature.com/articles/s42004-023-01074-2)

    Chen, Z.-X.; Hu, J.*; Zhi, Y.; Wu, C.-X.; Tian, S. X.* Ion-velocity imaging study of dissociative charge exchange reactions between Ar+ and trans-/cis-dichloroethylene. Chinese Journal of Chemical Physics 2023, 36: 509-516.

    Xie, J.; Fan, M.; Gao, X.-F.; Wu, B.; Wang, K.*; Tian, S. X.* Dissociation dynamics of anionic carbon monoxide in dark states. Journal of Chemical Physics (Communication) 2023, 158: 181101.

    Xie, J.; Fan, M.; Tian, S. X.* Dissociation dynamics of anionic nitrogen dioxide in the low-lying resonant states. Journal of Physical Chemistry Letters 2023, 14: 598-603.

    Chen, Z.; Li, Z.; Hu, J.; Tian, S. X.* Electron impact with the liquid-vapor interface. Accounts of Chemical Research 2022, 55: 3071-3079.

    Li, Z.†; Fu, C.-F.†; Chen, Z.; Tong, T.; Hu, J.; Yang, J.*; Tian, S. X.* Electron-induced synthesis of dimethyl ether in the liquid-vapor interface of methanol. Journal of Physical Chemistry Letters 2022, 13: 5220-5225.

    Fan, M.; Xie, J.; Gao, X.-F.; Wu, B.; Zhao, M.; Tian, S. X.* Dissociation dynamics of anionic carbon dioxide in the shape resonant state 2Πu. Journal of Physical Chemistry A 2022, 126: 3543−3548 (an invited article of Paul L. Houston Festschrift virtual special Issue).

    胡婕; 田善喜* 低能离子-分子反应动力学的研究进展《化学学报》(研究评论) 2022, 80(4): 535-541 (庆祝中国科学院青年创新促进会十年华诞). Hu, J.; Tian, S. X.* Progresses in the study of low-energy ion-molecule reaction dynamics. Acta Chimica Sinica 2022, 80: 535-541 (Account; DOI: 10.6023/A21120584).

    Hu, J.†; Zhi, Y.†; Xie, J.-C.; Wu, C.-X.; Tian, S. X.* Collision-energy dependent stereodynamics of the dissociative charge exchange reaction between Ar+ and CO. Journal of Physical Chemistry Letters 2021, 12: 7127-7133.

    Hu, J.; Xie, J.-C.; Wu, C.-X.; Tian, S. X.* Superposition-state N2+ produced in the intermolecular charge transfer from Ar+ to N2. Journal of Chemical Physics 2021, 154: 234303 (selected as Editor's Pick).

    Zhi, Y.; Hu, J.; Xie, J.-C.; Tian, S. X.* Ion-molecule charge exchange reactions between Ar+ and trans-/cis-dichloroethylene. Journal of Physical Chemistry A 2021, 125: 2573-2580. (a contribution article of Cheuk-Yiu Ng Festschrift Virtual Special Issue)

    Hu, J.; Wu, C.-X.; Zhi, Y.; Xie, J.-C.; He, M.-M.; Tian, S. X.* Stereodynamics observed in the reactive collisions of low-energy Ar+ with randomly oriented O2. Journal of Physical Chemistry Letters 2021, 12: 1346-1351.

    Li, Z.; Chen, Z.; Hu, J.; Li, H.; Tian, S. X.* A new experimental method for investigations on the microstructure of liquid-vapor interface. Chinese Journal of Chemical Physics 2021, 34: 43-50. (An invited review of the special issue on New Advanced Experimental Techniques on Chemical Physics).

    Gao, X. -F.; Xie, J.-C.; Li, H.; Meng, X.; Wu, Y.; Tian, S. X.* Direct observation of long-lived cyanide anions in superexcited states. Communications Chemistry 2021, 4: 13. (open access, https://www.nature.com/articles/s42004-021-00450-0)

    Gao, X. -F.†; An, F.†; Li, H.; Xie, J.-C.; Wang, X.-D.; Meng, X.; Wu, B.; Xie, D.-Q.*; Tian, S. X.* Probing the potential energy surfaces of BrCN¯ by dissociative electron attachment. Journal of Physical Chemistry Letters 2020, 11: 9110-9116.

    Wu, B; Wang, X.-D.; Gao, X.-F.; Li, H.; Tian, S. X.* Dissociative electron attachment to carbon dioxide. Chinese Journal of Chemical Physics 2020, 33: 521-531. (An invited review of the special issue on the Chinese Chemical Society's 16th National Chemical Dynamics Symposium).

    Chen, Z.; Fu, C.-F.; Li, Z.; Hu, J.; Li, H.; Yang, J.; Tian, S. X.* Identifying the molecular orientation and clusters in the liquid-vapor interface of 1-propanol by time-delayed mass spectrometry. Journal of Physical Chemistry Letters 2020, 11: 7510-7516.

    Meng, X.; Wu, B.; Gao, X.-F.; Xie, J.-C.; Li, H.; Yu, Y.; Zhao, D.; Tian, S. X.* Vibrationally-resolved photoemissions of N2 (3Πu →a3Πg) and CO (b3Σ+ →a3Π) by low-energy electron impacts. Journal of Chemical Physics 2020, 153: 024301.

    Wang, X.-D.; Gao, X.-F.; Li, H.; Wu, B.; Tian, S. X.* Dissociative electron attachment to polyatomic molecules. Journal of Physics: Conference Series 2020, 1412: 052010.

    He, M.-M.; Hu, J.; Wu, C.-X.; Zhi, Y.; Tian, S. X.* Collison-energy dependence of the ion-molecule charge exchange reaction Ar+ + CO → Ar + CO+. Journal of Physical Chemistry A 2020, 124: 3358-3363.

    Wu, C.-X.; Hu, J.; He, M.-M.; Zhi, Y.; Tian, S. X.* Ion momentum imaging study of the ion-molecule reaction Ar+ + O2 → Ar + O2+. Physical Chemistry Chemical Physics 2020, 22: 4640-4646.

    Gao, X.-F.; Li, H.; Meng, X.; Xie, J.-C.; Tian, S. X.* Synchronous and asynchronous dynamics of the concerted three-body dissociations of temporary negative ion CH2F2-. Journal of Chemical Physics 2020, 152: 084305 (Selected as Editor's Pick).

    Li, H.; Gao, X.-F.; Meng, X.; Tian, S. X.* Dissociative electron attachment to molecular acetonitrile. Journal of Physical Chemistry A 2019, 123: 9089-9095.

    Wu, C.-X.; Hu, J.; He, M.-M.; Tian, S. X.* Ion momentum imaging study of the ion-molecule charge exchange reaction of Ar+ + CO2. Journal of Physical Chemistry A 2019, 123: 8536-8541.

    Li, H.; Gao, X.-F.; Meng, X.; Tian, S. X.* Dissociative electron attachment to vibrationally excited CO2. Physical Review A 2019, 99: 032703.

    Gao, X.-F.; Li, H.; Meng, X.; Tian, S. X.* Ion-pair dissociations of BrCN by electron impacts. Chinese Journal of Chemical Physics 2019, 32: 89-92. (Dedicated to Professor Kopin Liu on the occasion of his 70th birthday)

    Hu, J.; Wu, C.-X.; Ma, Y.-S.; Tian, S. X.* Collision-energy dependence of the ion-molecule charge exchange reaction Ar+ + NO. Journal of Physical Chemistry A 2018, 122: 9171-9176.

    Chen, L.; Chen, Z.; Li, Z.; Hu, J.; Tian, S. X.* Time-delayed mass spectrometry of the low-energy electron impact with a liquid beam surface. Review of Scientific Instruments 2018, 89: 103102.

    Hu, J.; Wu, C.-X.; Tian, S. X.* A well-confined pulsed low-energy ion beam: Test experiments of Ar+. Review of Scientific Instruments 2018, 89: 066104.

    Wang, Y.-F.*; Tian, S. X. Low-energy electron attachment to serine conformers: Shape resonances and dissociation dynamics. Chinese Journal of Chemical Physics 2017, 30: 173-185.

    Ye, Y-.F.; Fu, C-.F.; Tian, S. X.* A molecular dynamics simulation study of ClF in water: Halogen bonding interaction in liquid. Chinese Journal of Chemical Physics 2017, 30: 25-28.

    Li, M.-Y.; Gao, X.-F.; Wang, X.-D.; Li, H.; Tian, S. X.* S- velocity images of dissociative electron attachment to OCS. International Journal of Mass Spectrometry 2016, 404: 20-23.

    Feng, W.-L.; Tian, S. X.* Ab initio molecular dynamics simulation study of dissociative electron attachment to C6H5(CH2)nCl (n = 0, 1, 2, 3, 4). International Journal of Mass Spectrometry 2016, 399-400: 40-43.

    Wang, X.-D.; Gao, X.-F.; Xuan, C.-J., Tian, S. X.* Dissociative electron attachment to CO2 produces molecular oxygen. Nature Chemistry 2016, 8: 258-263.

    Tian, S. X.*; Luo, Y. Reply to "Comment on 'Coherent interference in the resonant dissociative electron attachment to carbon monoxide'". Physical Review A 2015, 91: 056702.

    Wang, X.-D.; Xuan, C.-J.; Luo, Y.; Tian, S. X.* Coherent resonances observed in the dissociative electron attachment to carbon monoxide. Journal of Chemical Physics 2015, 143: 066101.

    Feng, W.-L.; Tian, S. X.* Ab initio molecular dynamics simulation study of dissociative electron attachment to dialanine conformers. Journal of Physical Chemistry A 2015, 119: 1838-1845.

    Wang, X.-D.; Xuan, C.-J.; Feng, W.-L.; Tian, S. X.* Dissociative electron attachments to ethanol and acetaldehyde: A combined experimental and simulation study. Journal of Chemical Physics 2015, 142: 064316.

    Xuan, C.-J.; Wang, X.-D.; Xia, L.; Wu, B.; Li, H.; Tian, S. X.* Dissociative electron attachment to 1,2-dichlorobenzene by using mass spectrometry with phosphor screen. Chinese Journal of Chemical Physics 2014, 27: 628-630.

    Fu, C.-F.; Tian, S. X.* Different aggregation dynamics of the benzene-water mixtures. Physical Chemistry and Chemical Physics 2014, 16: 21957-21963.

    Xia, L.; Wang, X.-D.; Xuan, C.-J.; Zeng, X.-J.; Li, H.-K.; Tian, S. X.*; Pan, Y.; Lau, K.-C.* State mixing by spin-orbit coupling of the anionic chloroiodine dissociations. Journal of Chemical Physics (Communication) 2014, 140: 041106.

    Yan, S.; Zhang, P.; Ma, X.*; Xu, S.; Tian, S. X.; Li, B.; Zhu, X. L.; Feng, W. T.; Zhao, D. M. Dissociation of the Ar trimer induced by a third atom in high-energy electron-impact ionization. Physical Review A 2014, 89: 062707.

    Tian, S. X.*; Wu, B.; Xia, L.; Li, H.-K.; Zeng, X.-J.; Luo, Y.; Yang, J. L. Coherent interference in the resonant dissociative electron attachment to carbon monoxide. Physical Review A 2013, 88: 012708.

    Fu, C.-F.; Tian, S. X.* Thermodynamics of ammonia and ammonium ion at the aqueous solution-air interfaces. Journal of Physical Chemistry C 2013, 117: 13011-13020.

    Li, H.-K.; Xia, L.; Zeng, X.-J.; Tian, S. X.* Two- and three-body dissociation dynamics of temporary negative ion NF3-. Journal of Physical Chemistry A 2013, 117: 3176-3182.

    Chu, G.B.; Chen, J; Liu, F.Y.*; Shan, X.B.; Sheng, L.S.; Xu, Y.F.; Tian, S. X. Positive and negative photoion spectroscopy study of C2Cl4. Molecular Physics 2013, 111: 427-435.

    Zeng, X.-J.; Xia, L.; Li, H.-K.; Lau, K.-C.; Tian, S. X.* Anion velocity imaging study of the dissociative electron attachment to CFCl3. Physical Review A 2013, 87: 012711. Selected into 'Kaleidoscope' of PRA Journal web site (January, 2013).

    Xia, L.; Zeng, X.-J.; Li, H.-K.; Wu, B.; Tian, S. X.* Orientation effect in the low-energy electron attachment to the apolar carbon tetrafluoride molecule. Angewandte Chemie, International Edition (Communication) 2013, 52: 1013-1016.

    Xia, L.; Wu, B.; Li, H.-K.; Zeng, X.-J.; Tian, S. X.* Imaging the indirect dissociation dynamics of temporary negative ion: N2O- -> N2 + O-. Journal of Chemical Physics (Communication) 2012, 137: 151102 (4 pages). One of the journal's Top 20 most read articles, in Oct. 2012.

    Wu, B.; Xia, L.; Wang, Y.-F.; Li, H.-K.; Zeng, X.-J.; Tian, S. X.* Renner-Teller effect on dissociative electron attachments to carbon dioxide. Physical Review A 2012, 85: 052709.

    Tian, S. X. Photoion-pair dissociation dynamics of polyatomic molecules with synchrotron radiation. Physical Chemistry Chemical Physics 2012, 14: 6433-6443 (Perspective Article).

    Wang, Y.-F.; Tian, S. X.* Low-energy electron collisions with formamide using the R-matrix method. Physical Review A 2012, 85: 012706.

    Wu, B.; Xia, L.; Li, H.-K.; Zeng, X.-J.; Tian, S. X.* Positive / negative ion velocity mapping apparatus for electron-molecule reactions. Review of Scientific Instruments 2012, 83: 013108.

    Contact

    Department of Chemical Physics, USTC
    96 Jinzhai Road, Hefei City, Anhui 230026
    China
    Office Phone: (+86) 551 63606465
    Lab Phone: (+86) 551 63606744
    Email: sxtian@ustc.edu.cn

    分子立体反应动力学实验室

    研究组成员隶属于中国科技大学化学物理系和合肥微尺度物质科学国家研究中心。目前的研究方向是“化学动力学”,包括:气相分子的电子贴附解离和低能量离子碰撞反应动力学,液体(含溶液)的气液界面微观反应机制以及用于四维透射电镜的超快相干电子束技术。 上述研究为大气化学、星际化学、生物分子结构、溶液化学合成等方面提供微观物理化学模型和先进技术。

    研究内容

    化学物质的起源 :星际空间中某些特殊分子、自由基、离子的产生和化学演化机制,行星(包括四万亿年前的地球)大气中氧气、水以及氨基酸、糖、核酸分子等生命相关基本物质的产生,分子手性的起源及其物理化学过程等。其中,我们组在2016年报道了“氧气起源”全新机制(入选百度百科词条“氧气”、编入科普中国“氧气的起源”等),2023年又发现了与太阳风相关的氧气产生新机制。

    原子分子新概念与反应动力学:电子-分子共振态的量子相干、负离子超激发态、负离子暗态动力学、气液界面的电子诱导反应、反常同位素动力学(dynamics)效应、溶剂化电子动力学等。

    先进方法与技术:气液界面原位质谱(时间延迟质谱)新方法、新型液相光电子能谱、超快量子相干电子束技术等。

    研究方法

    主要设备:电子-分子碰撞(贴附)解离的高分辨离子速度成像谱仪和光谱采集系统(自制)、离子-分子反应的离子速度成像谱仪(自制)、电子/离子与液体表面分子反应的质谱装置(自制)、针尖发射超快相干光电子系统(待研制)、四维透射电镜(待研制)。

    关键技术:低能量脉冲电子束(0-30eV、纳秒级脉冲宽度)、低能量脉冲离子束(0-60eV、纳秒-微秒脉冲宽度)、三维离子速度成像、微流喷射(microjet)液体束、微纳流动液体片(liquid sheet)、时间延迟质谱、超快(飞秒-皮秒脉冲宽度)相干电子束。