Synchrotron SOLEIL, l'Orme des Merisiers, Saint Aubin BP 48, 91192 Gif sur Yvette Cedex, France.
J Phys Chem A. 2021 Jun 10;125(22):4882-4887. doi: 10.1021/acs.jpca.1c03201. Epub 2021 May 24.
Hydrogen bonds and proton transfer reactions can be considered as being at the very heart of aqueous chemistry and of utmost importance for many processes of biological relevance. Nevertheless, these processes are not yet well understood, even in seemingly simple model systems like small water clusters. We present a study of the photoelectron spectrum of the water dimer, revealing previously unresolved vibrational structure with 10-30 meV (80-242 cm) typical splitting, in disagreement with a previous theoretical photoionization study predicting an apparent main vibrational progression with an ∼130 meV spacing [Kamarchik et al.; 2010, 132, 194311]. The observed vibrational structure and its deviation from the theoretical prediction is discussed in terms of known difficulties with calculations of strongly coupled anharmonic systems involving large amplitude motions. Potential contributions of the nonzero vibrational energy of the neutral water dimer at a finite experimental internal temperature are addressed. The internal temperature is estimated from the breakdown diagram associated with the dissociative ionization of the water dimer to be around to 130 K. This analysis also provides two additional, independently measured values for the 0 K appearance energy of the hydronium ion (HO) from dissociative ionization of the water dimer.
氢键和质子转移反应可以被认为是水相化学的核心，对许多与生物学相关的过程至关重要。然而，即使在像小分子水簇这样看似简单的模型体系中，这些过程也尚未得到很好的理解。我们研究了水二聚体的光电子能谱，揭示了以前未解决的振动结构，其典型分裂为 10-30 meV（80-242 cm），与之前预测具有约 130 meV 间距的明显主要振动进展的理论光致电离研究结果不一致[Kamarchik 等人；2010 年，132,194311]。根据已知的强耦合非谐系统计算中涉及大振幅运动的困难，讨论了观察到的振动结构及其与理论预测的偏差。讨论了在有限的实验内部温度下中性水二聚体的非零振动能量对其的潜在贡献。内部温度是根据水二聚体的离解性电离与断裂图估计的，约为 130 K。该分析还提供了两个额外的、独立测量的、由水二聚体的离解性电离产生的水合氢离子（HO）的 0 K 出现能的值。
