太赫兹泵浦液态水的XUV光电子能谱模拟
Simulated XUV Photoelectron Spectra of THz-pumped Liquid Water
摘要：
高强度的亚皮秒太赫兹（THz）脉冲可用于在液态水中诱导超快温度跳跃（T跳跃）。建立了具有液体密度的气体状水的超临界状态，预计伴随的结构变化将引起随时间变化的化学位移。我们研究了利用极紫外（XUV）光电子能谱学作为探测器的亚皮秒THz脉冲的强度和频率变化引起的超快动力学的可能性。为此，我们使用从头计算方法计算（H2O）$_{20}$团簇嵌入在水环境中的点电荷表示的光电离截面和光电子能量。团簇的几何形状从从头算分子动力学模拟太赫兹-水相互作用建模采样。我们发现，在价光电子能谱的峰值被移动高达0.4 eV的泵浦脉冲后，它们被扩大相对于未加热的水。这些变化可能与加热引起的结构变化有关，但由于饱和效应，它们不足以作为T跃变水的温度计。
英文摘要：
Highly intense, sub-picosecond terahertz (THz) pulses can be used to induce ultrafast temperature jumps (T-jumps) in liquid water. A supercritical state of gas-like water with liquid density is established, and the accompanying structural changes are expected to give rise to time-dependent chemical shifts. We investigate the possibility of using extreme ultraviolet (XUV) photoelectron spectroscopy as a probe for ultrafast dynamics induced by sub-picosecond THz pulses of varying intensities and frequencies. To this end, we use ab initio methods to calculate photoionization cross sections and photoelectron energies of (H2O)$_{20}$ clusters embedded in an aqueous environment represented by point charges. The cluster geometries are sampled from ab initio molecular dynamics simulations modeling the THz-water interactions. We find that the peaks in the valence photoelectron spectrum are shifted by up to 0.4 eV after the pump pulse, and that they are broadened with respect to unheated water. The shifts can be connected to structural changes caused by the heating, but due to saturation effects they are not sensitive enough to serve as a thermometer for T-jumped water.
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