Aggregation-Induced Dissociation of HCl(H2O)4 Below 1 K: The Smallest Droplet of Acid
Aggregation-Induced Dissociation of HCl(H2O)4 Below 1 K: The Smallest Droplet of Acid
复制标题
DOI：
10.1126/science.1171753
复制
发表时间：
2009-06-19
期刊：
影响因子：
56.9
通讯作者：
Marx, Dominik
中科院分区：
文献类型：
--
作者：
Gutberlet, Anna;Schwaab, Gerhard;Marx, Dominik
纳米环境中带电碎片在超冷温度下的酸解离和随后的溶剂化，与周围的散装水不同，与大气和星际化学有关，但仍然知之甚少。在这里，我们报告了在0.37开尔文的超流氦团簇中形成的纳米级酸液滴的实验观察。高分辨率质量选择红外激光光谱揭示了HCl酸与水分子的连续聚集，HCl(H2O)(n)很容易在n = 4时形成水合氢离子。伴随的从头算模拟表明，未解离的团簇通过逐步加入水分子在静电转向排列中组装到n = 3。在环状未解离的HCl(H2O)(3)中加入第四个水分子，然后自发地产生紧凑的解离的h30 +(H2O)(3)Cl-离子对。这种聚集机制绕过了n = 4势能表面的深层局部能量最小值，并为超冷温度下的反应性提供了一般范例。
Acid dissociation and the subsequent solvation of the charged fragments at ultracold temperatures in nanoenvironments, as distinct from ambient bulk water, are relevant to atmospheric and interstellar chemistry but remain poorly understood. Here we report the experimental observation of a nanoscopic aqueous droplet of acid formed within a superfluid helium cluster at 0.37 kelvin. High-resolution mass-selective infrared laser spectroscopy reveals that successive aggregation of the acid HCl with water molecules, HCl(H2O)(n), readily results in the formation of hydronium at n = 4. Accompanying ab initio simulations show that undissociated clusters assemble by stepwise water molecule addition in electrostatic steering arrangements up to n = 3. Adding a fourth water molecule to the ringlike undissociated HCl(H2O)(3) then spontaneously yields the compact dissociated H3O+(H2O)(3)Cl- ion pair. This aggregation mechanism bypasses deep local energy minima on the n = 4 potential energy surface and offers a general paradigm for reactivity at ultracold temperatures.