Hydrated ions are ubiquitous in environmental and biological media. Understanding the perturbation exerted by an ion on the water hydrogen bond network is possible in the nanodrop regime by recording vibrational spectra in the O–H bond stretching region. This has been achieved experimentally in recent years by forming gaseous ions containing tens to hundreds of water molecules and recording their infrared photodissociation spectra. In this paper, we demonstrate the capabilities of a modeling strategy based on an extension of the AMOEBA polarizable force field to implement water atomic charge fluctuations along with those of intramolecular structure along the dynamics. This supplementary flexibility of nonbonded interactions improves the description of the hydrogen bond network and, therefore, the spectroscopic response. Finite temperature IR spectra are obtained from molecular dynamics simulations by computing the Fourier transform of the dipole moment autocorrelation function. Simulations of 1–2 ns are required for extensive sampling in order to reproduce the experimental spectra. Furthermore, bands are assigned with the driven molecular dynamics approach. This method package is shown to compare successfully with experimental spectra for 11 ions in water drops containing 36–100 water molecules. In particular, band frequency shifts of the free O–H stretching modes at the cluster surface are well reproduced as a function of both ion charge and drop size.

中文翻译：

---

含离子水滴红外光谱建模策略

水合离子在环境和生物介质中无处不在。通过记录O–H键拉伸区域的振动光谱，可以了解在纳米液滴状态下离子对水氢键网络施加的扰动。近年来，通过形成包含数十到数百个水分子的气态离子并记录其红外光解离光谱，已通过实验实现了这一点。在本文中，我们演示了基于AMOEBA可极化力场扩展的建模策略的功能，该功能可以实现水原子电荷波动以及沿着分子动力学的分子内结构波动。非键相互作用的这种补充灵活性改善了对氢键网络的描述，从而改善了光谱响应。通过计算偶极矩自相关函数的傅立叶变换，从分子动力学模拟中获得有限的温度IR光谱。大量采样需要模拟1–2 ns，以重现实验光谱。此外，通过驱动分子动力学方法为谱带分配。该方法包已成功与包含36–100个水分子的水滴中的11个离子的实验光谱进行了比较。尤其是，在簇表面自由OH拉伸模式的带频移被很好地再现为离子电荷和液滴尺寸的函数。大量采样需要模拟1–2 ns，以重现实验光谱。此外，通过驱动分子动力学方法为谱带分配。该方法包已成功与包含36–100个水分子的水滴中的11个离子的实验光谱进行了比较。尤其是，在簇表面自由O–H拉伸模式的带频移作为离子电荷和液滴尺寸的函数得到了很好的再现。大量采样需要模拟1–2 ns，以重现实验光谱。此外，通过驱动分子动力学方法为谱带分配。该方法包已成功与包含36–100个水分子的水滴中的11个离子的实验光谱进行了比较。尤其是，在簇表面自由O–H拉伸模式的带频移作为离子电荷和液滴尺寸的函数得到了很好的再现。