Velocity Map Imaging Spectrometer for Studying the Atomic Cluster Thermodynamics
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摘要: 原子团簇的激发温度可由反应产物（出射电子或碎片）的初始平动能这一可观测量间接获得，为了提高原子团簇激发温度的测量精度，设计并搭建了一套具有高动能分辨的离子速度成像谱仪。本谱仪的高动能分辨性能首先借助Simion8.0软件优化静电透镜和分子束限束装置的几何结构来实现，然后通过理论模拟证明本套谱仪具有预期好的动能分辨能力。设备搭建完成后，研究了C60分子束在纳秒激光场中发生的延迟电离过程，获得了C60+离子随延迟时间增加而逐渐变窄的二维时间切片图像。分析表明，激光脉冲产生的多个C60+离子间的库仑耦合作用将会扩展二维切片图像的横向分布，提取库仑耦合作用对C60+离子初始平动能的影响，并通过分析C60+离子间的库仑耦合随延迟时间增加而逐渐变弱的定量依赖关系，证实了本套谱仪具有了设计预期的高动能分辨能力。这一工作为下一步基于离子速度成像技术细致研究分子热力学的相关课题提供技术参考。
Excitation temperature of fragmenting atomic clusters can been extracted from the initial kinetic energies of ionic products. To improve the accuracy of the temperature measurements, we have designed an ionic velocity map imaging spectrometer with high kinetic energy resolution. Firstly, based on the simulations using Simion8.0 software, the high resolution is obtained by adjusting the structure of the electrostatic lenses and collimation of molecular beam. According to theoretical analysis, it is proved that the spectrometer has a well defined kinetic energy resolution. Then, we have studied the delay ionization processes of C60 induced by nanosecond laser. A series of narrowed two-dimensional time-sliced velocity images of the C60+ with increasing the delayed time were recorded. Analysis revealed that Coulomb force between C60+ clusters in same laser shots will broadening the transverse distribution of 2D image. Considering the influence of Coulomb force on initial kinetic energy of C60+ clusters, the high resolution has been proved by analysing the negative relationship between Coulomb force and delayed time. It indicates that the establishment of the spectrometer builds up a good basis for next experiments on the studies for molecular thermodynamics in atomic clusters.Abstract: Excitation temperature of fragmenting atomic clusters can been extracted from the initial kinetic energies of ionic products. To improve the accuracy of the temperature measurements, we have designed an ionic velocity map imaging spectrometer with high kinetic energy resolution. Firstly, based on the simulations using Simion8.0 software, the high resolution is obtained by adjusting the structure of the electrostatic lenses and collimation of molecular beam. According to theoretical analysis, it is proved that the spectrometer has a well defined kinetic energy resolution. Then, we have studied the delay ionization processes of C60 induced by nanosecond laser. A series of narrowed two-dimensional time-sliced velocity images of the C60+ with increasing the delayed time were recorded. Analysis revealed that Coulomb force between C60+ clusters in same laser shots will broadening the transverse distribution of 2D image. Considering the influence of Coulomb force on initial kinetic energy of C60+ clusters, the high resolution has been proved by analysing the negative relationship between Coulomb force and delayed time. It indicates that the establishment of the spectrometer builds up a good basis for next experiments on the studies for molecular thermodynamics in atomic clusters. -
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