Time-resolved photoelectron imaging of azulene

甘菊环的时间分辨光电子成像

• 批准号: EP/H006354/1
• 负责人: John Whitaker
• 金额: $ 2.6万
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2009
• 资助国家: 英国
• 起止时间: 2009 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FH006354%2F1
• 关键词: Time; resolved; photoelectron; imaging; azulene

Within the framework of Koopmans' theorem we can loosely interpret photoelectron spectra as a measure of the binding energy of electrons in occupied molecular orbitals and it is of interest to ask what can one learn from the measurement of transient photoelectron signals obtained through the course of a chemical reaction. Can we, for example, follow configurational changes in the active electrons of a photochemical or thermal ring opening reaction? Can we distinguish concerted from sequential bond formation or rupture? To what extent does electron-electron correlation (the configuration interaction) blur the picture? Detailed investigation into the mechanisms by which optical energy is transformed into other forms of energy, electrical and mechanical, is of great relevance to developing a fundamental understanding of many important phenomena from photobiology (e.g. vision) to nanotechnology (e.g. molecular ratchets). Cleary, in order to be able do this we require an instrument which can follow changes in the photoelectrum spectrum on the time-scale of a chemical reaction; which maybe as fast as tens of femtoseconds (one femtosecond is 1 thousanth of a millionth of a millionth of a second). Time-resolved photo-electron imaging spectroscopy (TRPEIS) is an emerging technique with which to study such photochemistry. The method is based on a marriage of pump-probe spectroscopy to charged particle imaging. A short pulse on the femtosecond time-scale is used to excite a non-stationary state of a molecule. The time evolution is probed by a second time delayed pulse which is used to ionize the molecule, and the resulting photoelectron is detected with a position sensitive detector at the end of a time-of-flight mass spectrometer. The electron is guided to the detector by means of an electrostatic immersion lens placed around the laser-molecule interaction zone. The lens has the property of focusing the charged particle's velocity vector onto the surface of the detector. Obviously by reversing the bias of the extracting electrodes the device can just as easily be configured to detect photoions, but there is generally more information in the photoelectron energy spectrum.We have used this method to study the photochemistry of a number of molecules (e.g. nitrogen dioxide, pryrazine, azulene) and have observed a number of interesting phenomena such as coherent wavepacket motion (both vibrational and rotational). Azulene turns out to exhibit a particularly interesting ionization behaviour but until now we have not had the temporal resolution to really unravel the dynamics. With this proposal our ambition is to push the time resolution of our experiment to 25 fs or better.

在Koopmans定理的框架内，我们可以粗略地将光电子能谱解释为电子在占据的分子轨道中的结合能的量度，并且有趣的是，人们可以从通过化学反应过程获得的瞬态光电子信号的测量中学到什么。例如，我们能否跟踪光化学或热开环反应中活性电子的构型变化？我们能区分协同键的形成和连续键的断裂吗？电子-电子关联（组态相互作用）在多大程度上模糊了图像？详细研究光能转化为其他形式的能量（电能和机械能）的机制，对于从光生物学（例如视觉）到纳米技术（例如分子棘轮）的许多重要现象的基本理解具有重要意义。显然，为了能够做到这一点，我们需要一种仪器，它可以在化学反应的时间尺度上跟踪光银光谱的变化;这可能快到几十飞秒（一飞秒是百万分之一秒的千分之一）。时间分辨光电子成像光谱（TRPEIS）是一种新兴的技术与研究这种光化学。该方法是基于婚姻的泵探测光谱带电粒子成像。飞秒时间尺度上的短脉冲用于激发分子的非稳态。时间演化是由第二个时间延迟的脉冲，这是用来探测的分子，和所产生的光电子的位置敏感检测器在飞行时间质谱仪的末端检测。电子通过放置在激光分子相互作用区周围的静电浸没透镜引导到检测器。透镜具有将带电粒子的速度矢量聚焦到检测器表面上的特性。显然，通过反转的提取电极的偏置的设备可以很容易地配置为检测光离子，但通常有更多的信息在光电子的能量spectrum.We使用这种方法来研究的光化学的一些分子（例如二氧化氮，pryrazine，甘菊环），并观察到一些有趣的现象，如相干波包运动（振动和旋转）。甘菊环表现出一种特别有趣的电离行为，但到目前为止，我们还没有时间分辨率来真正解开动力学。有了这个提议，我们的目标是将我们实验的时间分辨率提高到25 fs或更高。