Photoelectron photoion coincidence imaging of ultrafast control in multichannel molecular dynamics.
Photoelectron photoion coincidence imaging of ultrafast control in multichannel molecular dynamics.
复制标题
多通道分子动力学超快控制的光电子光离子符合成像。
作者：
C. S. Lehmann;N. B. Ram;D. Irimia;M. Janssen
利用飞秒脉冲整形和速度图光电子光离子符合成像技术研究了CF 3 I多通道离子碎裂动力学的控制。当CF 3 I被540 nm左右的飞秒激光脉冲光激发时，在飞行时间质谱中观察到两个主要离子，母CF 3 I+离子和CF 3+碎片离子。在这第一项研究中，我们集中在液晶形状的激光脉冲的影响上的分子动力学。使用单个飞行时间延迟线探测器对电子和离子的三维反冲分布进行重合成像。通过在检测到电子之后快速切换各种速度图离子透镜上的电压，用相同的成像检测器测量电子和重合离子两者。这些结果表明，使用切换的透镜电压在原理上可以显著简化光电子-光离子符合成像设备。据观察，啁啾脉冲、双脉冲和多脉冲等成形激光场可以将CF 3 + CF 3 I+比率提高高达100%。的总能量的动力学揭示了一致的光电子能谱和CF 3+和I片段的动能分析。母体CF 3 I+和CF 3+碎片都是由五光子激发过程产生的。碎片是以非常低的动能形成的。光电子能谱和CF ~（3+）/CF ~（3 I+）比值随整形激光脉冲中心波长的变化而变化。当脉冲间隔为60 fs时，观察到双脉冲激发的CF 3 +/CF 3 I+比约60%的最佳增强。我们建议，控制机制是由中性激发态的动态，我们讨论的结果有关的电子激发（里德伯）状态的CF 3 I的位置。
The control of multichannel ionic fragmentation dynamics in CF3I is studied by femtosecond pulse shaping and velocity map photoelectron photoion coincidence imaging. When CF3I is photoexcited with femtosecond laser pulses around 540 nm there are two major ions observed in the time-of-flight mass spectrum, the parent CF3I+ ion and the CF3+ fragment ion. In this first study we focussed on the influence of LCD-shaped laser pulses on the molecular dynamics. The three-dimensional recoil distribution of electrons and ions were imaged in coincidence using a single time-of-flight delay line detector. By fast switching of the voltages on the various velocity map ion lenses after detection of the electron, both the electron and the coincident ion are measured with the same imaging detector. These results demonstrate that a significant simplification of a photoelectron-photoion coincidence imaging apparatus is in principle possible using switched lens voltages. It is observed that shaped laser fields like chirped pulses, double pulses, and multiple pulses can enhance the CF3+CF3I+ ratio by up to 100%. The total energetics of the dynamics is revealed by analysis of the coincident photoelectron spectra and the kinetic energy of the CF3+ and I fragments. Both the parent CF3I+ and the CF3+ fragment result from a five-photon excitation process. The fragments are formed with very low kinetic energy. The photoelectron spectra and CF3+/CF3I+ ratio vary with the center wavelength of the shaped laser pulses. An optimal enhancement of the CF3+/CF3I+ ratio by about 60% is observed for the double pulse excitation when the pulses are spaced 60 fs apart. We propose that the control mechanism is determined by dynamics on neutral excited states and we discuss the results in relation to the location of electronically excited (Rydberg) states of CF3I.