Center for Free-Electron Laser Science, DESY, Notkestrasse 85, 22607 Hamburg, Germany.
SLAC National Accelerator Laboratory, Stanford University, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
J Chem Phys. 2019 Jan 28;150(4):044505. doi: 10.1063/1.5054272.
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 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 (HO) 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.
高强度、亚皮秒太赫兹 (THz) 脉冲可用于在液态水中引发超快温度跃变 (T-jump)。建立了具有液体密度的类气体水的超临界状态，预计伴随的结构变化将导致与时间相关的化学位移。我们研究了使用极端紫外光电离光谱作为探测亚皮秒 THz 脉冲引起的超快动力学的可能性，这些脉冲的强度和频率不同。为此，我们使用从头算方法计算了嵌入在点电荷表示的水溶液中的 (HO) 团簇的光致电离截面和光电子能量。团簇的几何形状是从模拟 THz-水相互作用的从头算分子动力学模拟中采样得到的。我们发现，在泵浦脉冲之后，价光电谱中的峰值最多移动了 0.4 eV，并且相对于未加热的水，它们变宽了。这些位移可以与加热引起的结构变化联系起来，但由于饱和效应，它们不够敏感，无法用作 T-jump 水的温度计。
