Electronic structure of liquid water from polarization-dependent two-photon absorption spectroscopy
Electronic structure of liquid water from polarization-dependent two-photon absorption spectroscopy
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DOI：
10.1063/1.3078336
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发表时间：
2009-02-28
影响因子：
4.4
通讯作者：
Bradforth, Stephen E.
中科院分区：
文献类型：
--
作者：
Elles, Christopher G.;Rivera, Christopher A.;Bradforth, Stephen E.
在7至10 eV范围内的双光子吸收（2 PA）光谱为液态水的电子结构提供了新的见解。连续的2 PA光谱是通过泵浦-探测技术获得的，使用宽带探测脉冲同时记录多个波长的吸收。当泵浦光子能量从4.6 eV增加到6.2 eV时，观察到绝对2 PA截面的预共振增强。吸收截面还取决于泵浦光子和探测光子的相对偏振。整个光谱的偏振比的变化揭示了2 PA的详细图像，并表明至少有四个不同的跃迁在10 eV以下发挥作用。孤立分子的理论偏振比说明了在破译2 PA光谱的实验偏振测量的值，并提供了一个简单的模拟液体光谱的框架。一个更全面的模型超越了孤立的分子图像，并将2 PA光谱与以前的单光子吸收，光电子和X射线吸收光谱测量液体水连接起来。首次指定以前未解决的重叠过渡。最后，垂直激发态的电子特性与液态水的能量相关电离机制有关。
Two-photon absorption (2PA) spectroscopy in the range from 7 to 10 eV provides new insight on the electronic structure of liquid water. Continuous 2PA spectra are obtained via the pump-probe technique, using broadband probe pulses to record the absorption at many wavelengths simultaneously. A preresonance enhancement of the absolute 2PA cross section is observed when the pump-photon energy increases from 4.6 to 6.2 eV. The absorption cross section also depends on the relative polarization of the pump and probe photons. The variation of the polarization ratio across the spectrum reveals a detailed picture of the 2PA and indicates that at least four different transitions play a role below 10 eV. Theoretical polarization ratios for the isolated molecule illustrate the value of the experimental polarization measurement in deciphering the 2PA spectrum and provide the framework for a simple simulation of the liquid spectrum. A more comprehensive model goes beyond the isolated molecule picture and connects the 2PA spectrum with previous one-photon absorption, photoelectron, and x-ray absorption spectroscopy measurements of liquid water. Previously unresolved, overlapping transitions are assigned for the first time. Finally, the electronic character of the vertical excited states is related to the energy-dependent ionization mechanism of liquid water.