Department of Chemistry, Benedictine University, 5700 College Road, Lisle, Illinois 60532, USA.
Notre Dame Radiation Laboratory, Notre Dame, Indiana 46556, USA.
Nat Commun. 2017 May 17;8:15435. doi: 10.1038/ncomms15435.
The nature and extent of hydrogen bonding in water has been scrutinized for decades, including how it manifests in optical properties. Here we report vacuum ultraviolet absorption spectra for the lowest-lying electronic state of subcritical and supercritical water. For subcritical water, the spectrum redshifts considerably with increasing temperature, demonstrating the gradual breakdown of the hydrogen-bond network. Tuning the density at 381 °C gives insight into the extent of hydrogen bonding in supercritical water. The known gas-phase spectrum, including its vibronic structure, is duplicated in the low-density limit. With increasing density, the spectrum blueshifts and the vibronic structure is quenched as the water monomer becomes electronically perturbed. Fits to the supercritical water spectra demonstrate consistency with dimer/trimer fractions calculated from the water virial equation of state and equilibrium constants. Using the known water dimer interaction potential, we estimate the critical distance between molecules (ca. 4.5 Å) needed to explain the vibronic structure quenching.
几十年来，人们一直在仔细研究水中氢键的性质和程度，包括它在光学性质中的表现。在这里，我们报告了亚临界和超临界水的最低电子态的真空紫外吸收光谱。对于亚临界水，随着温度的升高，光谱明显红移，表明氢键网络逐渐破裂。在 381°C 时调节密度可以深入了解超临界水中氢键的程度。在低密度极限下，重现了已知的气相光谱，包括其振子结构。随着密度的增加，光谱蓝移，并且随着水单体受到电子干扰，振子结构被猝灭。对超临界水光谱的拟合表明，与从水维里状态方程和平衡常数计算得出的二聚体/三聚体分数一致。利用已知的水二聚体相互作用势能，我们估计了分子之间的临界距离（约 4.5Å），这需要解释振子结构猝灭。
