Photoelectron imaging of helium droplets doped with Xe and Kr atoms
Photoelectron imaging of helium droplets doped with Xe and Kr atoms
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DOI：
10.1021/jp802332f
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发表时间：
2008-10-02
影响因子：
2.9
通讯作者：
Neumark, Daniel M.
中科院分区：
文献类型：
--
作者：
Wang, Chia C.;Kornilov, Oleg;Neumark, Daniel M.
使用先进光源的 VUV 同步加速器辐射对掺杂 Xe 和 Kr 原子的氦液滴进行光电离，并测量所得的光电子图像。对各种 He 液滴尺寸、光子能量和掺杂剂拾取条件进行了研究。在 21.6 eV（He 液滴 2p P-1(1) 电子激发态的吸收最大值）处观察到掺杂剂的显着电离，表明通过激发转移的间接电离机制。光电子图像和光谱揭示了光电子逃离液滴的多种光电离机制和路径。具体来说，它们显示了一组尖锐的峰，这些峰被分配给 He* 掺杂剂彭宁电离的两种机制，其中光电子离开液滴而没有可检测到的能量损失，代表经历显着能量损失的电子的广泛而强烈的特征，以及可能由液滴表面的电子捕获而产生的少量超慢电子。宽阔、强烈的特征与液滴尺寸的相关性表明此处看到的最大液滴（<N>大约为 250,000）中导带边缘的发展。
Helium droplets doped with Xe and Kr atoms were photoionized by using VUV synchrotron radiation from the Advanced Light Source and the resulting photoelectron images were measured. A wide range of He droplet sizes, photon energies, and dopant pick-up conditions was investigated. Significant ionization of dopants was observed at 21.6 eV, the absorption maximum of 2p P-1(1) electronic excited state of He droplets, indicating an indirect ionization mechanism via excitation transfer. The photoelectron images and spectra reveal multiple photoionization mechanisms and pathways for the photoelectrons to escape the droplet. Specifically, they show sets of sharp peaks assigned to two mechanisms for Penning ionization of the dopant by He* in which the photoelectrons leave the droplet with no detectable energy loss, a broad, intense feature representing electrons that undergo significant energy loss, and a small amount of ultraslow electrons that may result from electron trapping at the droplet surface. The droplet-size dependence of the broad, intense feature suggests the development of the conduction band edge in the largest droplets seen here (< N > approximate to 250,000).