Novel Collective Autoionization Process Observed in Electron Spectra of He Clusters
Novel Collective Autoionization Process Observed in Electron Spectra of He Clusters
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DOI：
10.1103/physrevlett.112.073401
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发表时间：
2014-02-20
影响因子：
8.6
通讯作者：
Moeller, T.
中科院分区：
文献类型：
--
作者：
Ovcharenko, Y.;Lyamayev, V.;Moeller, T.
用光电子能谱研究了功率密度高达10(13)W/cm(2)的飞秒强紫外光脉冲辐照下He纳米液滴的电离动力学。氦液滴被共振激发到原子状的2p态，光子能量为21.4 eV，低于电离势(i-p)，直接进入42.8 eV光子的电离连续体。虽然在i-p以上直接电离后的电子发射在基于直接电子发射事件序列的模型中得到了很好的解释，但共振激发提供了涉及许多激发的原子状2p态的新的集体电离机制的证据。随着功率密度的增加，由原子间库仑衰变引起的直接光谱线消失。它表明，电离是由于至少三个激发原子之间在飞秒时间尺度上进行的能量交换而发生的。与最近的理论工作一致，这种新的电离过程是非常有效的，预计它对许多其他系统也有重要意义。
The ionization dynamics of He nanodroplets irradiated with intense femtosecond extreme ultraviolet pulses of up to 10(13) W/cm(2) power density have been investigated by photoelectron spectroscopy. Helium droplets were resonantly excited to atomiclike 2p states with a photon energy of 21.4 eV, below the ionization potential (I-p), and directly into the ionization continuum with 42.8 eV photons. While electron emission following direct ionization above I-p is well explained within a model based on a sequence of direct electron emission events, the resonant excitation provides evidence of a new, collective ionization mechanism involving many excited atomiclike 2p states. With increasing power density the direct photoline due to an interatomic Coulombic decay disappears. It indicates that ionization occurs due to energy exchange between at least three excited atoms proceeding on a femtosecond time scale. In agreement with recent theoretical work the novel ionization process is very efficient and it is expected to be important for many other systems.