Pérez de Tudela Ricardo, Marx Dominik
Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, 44780 Bochum, Germany.
Phys Rev Lett. 2017 Dec 1;119(22):223001. doi: 10.1103/PhysRevLett.119.223001. Epub 2017 Nov 28.
The dissociation of acids in aqueous environments at low temperatures in the presence of a limited amount of water is underlying a wealth of processes from atmospheric to interstellar science. For the paradigmatic case of HCl(H_{2}O)_{n} clusters, our extensive ab initio path integral simulations quantify in terms of free energy differences and barriers that n=4 water molecules are indeed required to dissociate HCl at low temperatures. Increasing the temperature, however, reverses the process and thus counteracts dissociation by fluctuation-driven recombination. The size of the electric dipole moment is shown to not correlate with the acid being in its dissociated or molecular state, thus rendering its measurement as a function of n unable to detect the dissociation transition.
在有限量水存在的情况下，低温时酸在水性环境中的解离是从大气科学到星际科学的众多过程的基础。对于HCl(H₂O)ₙ团簇的典型情况，我们广泛的从头算路径积分模拟根据自由能差和势垒量化得出，在低温下确实需要4个水分子才能使HCl解离。然而，温度升高会使过程逆转，从而通过涨落驱动的重组抵消解离。结果表明，电偶极矩的大小与酸处于解离态或分子态无关，因此将其作为n的函数进行测量无法检测到解离转变。
