Brünig Florian N, Rammler Manuel, Adams Ellen M, Havenith Martina, Netz Roland R
Freie Universität Berlin, Department of Physics, 14195, Berlin, Germany.
Ruhr-Universität Bochum, Department of Physical Chemistry II, 44780, Bochum, Germany.
Nat Commun. 2022 Jul 21;13(1):4210. doi: 10.1038/s41467-022-31700-x.
The theoretical basis for linking spectral signatures of hydrated excess protons with microscopic proton-transfer mechanisms has so far relied on normal-mode analysis. We introduce trajectory-decomposition techniques to analyze the excess-proton dynamics in ab initio molecular-dynamics simulations of aqueous hydrochloric-acid solutions beyond the normal-mode scenario. We show that the actual proton transfer between two water molecules involves for relatively large water-water separations crossing of a free-energy barrier and thus is not a normal mode, rather it is characterized by two non-vibrational time scales: Firstly, the broadly distributed waiting time for transfer to occur with a mean value of 200-300 fs, which leads to a broad and weak shoulder in the absorption spectrum around 100 cm, consistent with our experimental THz spectra. Secondly, the mean duration of a transfer event of about 14 fs, which produces a rather well-defined spectral contribution around 1200 cm and agrees in location and width with previous experimental mid-infrared spectra.
将水合过量质子的光谱特征与微观质子转移机制联系起来的理论基础，迄今为止一直依赖于简正模式分析。我们引入轨迹分解技术，以分析超出简正模式情形的盐酸水溶液从头算分子动力学模拟中的过量质子动力学。我们表明，两个水分子之间实际的质子转移涉及相对较大的水 - 水间距时跨越一个自由能垒，因此不是一个简正模式，而是由两个非振动时间尺度来表征：首先，转移发生的等待时间分布广泛，平均值为200 - 300飞秒，这导致在吸收光谱中约100厘米处出现一个宽而弱的肩峰，与我们的太赫兹实验光谱一致。其次，转移事件的平均持续时间约为14飞秒，这在约1200厘米处产生了一个相当明确的光谱贡献，并且在位置和宽度上与先前的实验中红外光谱一致。
