通过透射模式X射线吸收光谱在氧气K边缘探测液态水中的同位素效应,The Journal of Chemical Physics

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通过透射模式X射线吸收光谱在氧气K边缘探测液态水中的同位素效应
The Journal of Chemical Physics ( IF 3.1 ) Pub Date : 2016-09-08 13:07:07 , DOI: 10.1063/1.4962237
Simon Schreck _{1,

2} , Philippe Wernet ₁

Affiliation

通过在透射模式下测量的O K边缘处的X射线吸收光谱研究了液态水中同位素取代的影响。证实了较早的X射线拉曼散射实验，发现D ₂ O光谱相对于H ₂ O发生了蓝移，而D ₂ O光谱的展宽程度较小。根据对紫外线和X射线拉曼光谱的较早解释，位移与D ₂ O和H ₂之间的基态零点能量之差有关。O，而扩宽的差异与基态振动零点分布的差异有关。我们证明了传输模式的测量允许以前所未有的精度确定频谱形状。由于与以前的测量相比，除了光谱分辨率和信噪比提高之外，新数据还能够严格确定同位素取代后液态水的O边缘X射线吸收光谱中的蓝移和加宽。将结果与紫外线吸收数据进行比较，并讨论它们在多大程度上反映了液体基态中零点能量和振动零点分布的差异。最终状态势的形状的影响，包括弗兰克-康登结构，解决了液体中氢键环境不同产生的₂ O和D ₂ O问题。此外，我们还讨论了通过我们的传输模式测量和最新的X射线拉曼散射实验得出的水的O K边缘吸收光谱之间的差异。提出了实验提取的蓝移和展宽值，以作为计算液体H ₂ O和D ₂ O中的基态零点能量和振动零点分布的测试。这显然激发了对新计算的需求。液态水的O K边缘X射线吸收光谱图。

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Isotope effects in liquid water probed by transmission mode x-ray absorption spectroscopy at the oxygen K-edge

The effects of isotope substitution in liquid water are probed by x-ray absorption spectroscopy at the O K-edge as measured in transmission mode. Confirming earlier x-ray Raman scattering experiments, the D₂O spectrum is found to be blue shifted with respect to H₂O, and the D₂O spectrum to be less broadened. Following the earlier interpretations of UV and x-ray Raman spectra, the shift is related to the difference in ground-state zero-point energies between D₂O and H₂O, while the difference in broadening is related to the difference in ground-state vibrational zero-point distributions. We demonstrate that the transmission-mode measurements allow for determining the spectral shapes with unprecedented accuracy. Owing in addition to the increased spectral resolution and signal to noise ratio compared to the earlier measurements, the new data enable the stringent determination of blue shift and broadening in the O K-edge x-ray absorption spectrum of liquid water upon isotope substitution. The results are compared to UV absorption data, and it is discussed to which extent they reflect the differences in zero-point energies and vibrational zero-point distributions in the ground-states of the liquids. The influence of the shape of the final-state potential, inclusion of the Franck-Condon structure, and differences between liquid H₂O and D₂O resulting from different hydrogen-bond environments in the liquids are addressed. The differences between the O K-edge absorption spectra of water from our transmission-mode measurements and from the state-of-the-art x-ray Raman scattering experiments are discussed in addition. The experimentally extracted values of blue shift and broadening are proposed to serve as a test for calculations of ground-state zero-point energies and vibrational zero-point distributions in liquid H₂O and D₂O. This clearly motivates the need for new calculations of the O K-edge x-ray absorption spectrum of liquid water.

更新日期：2016-09-09

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