Probing ice-nucleation processes on the molecular level using second harmonic generation spectroscopy
Probing ice-nucleation processes on the molecular level using second harmonic generation spectroscopy
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DOI：
10.5194/amt-8-3519-2015
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发表时间：
2015-01-01
影响因子：
3.8
通讯作者：
Leisner, T.
中科院分区：
文献类型：
--
作者：
Abdelmonem, A.;Luetzenkirchen, J.;Leisner, T.
我们提出并描述了一种新的装置，将全内反射几何（TIR）中的二次谐波产生（SHG）光谱应用于非均质冻结研究。它允许在非均相冰成核之前，在低温下监测固体表面水结构的演变。除了研究温度依赖性的可能性之外，我们的设置中的一个主要新颖之处是能够直接测量TIR几何形状的片状样品。作为主要的实验结果，我们发现我们的方法可以区分好的和不好的冰成核表面。而在蓝宝石基面，已知是一个较差的冰核，在冻结前没有发现水分子的结构重排，云母的基面表面，类似于冰活性矿物粉尘的表面，在远高于冻结转变的温度下表现出强烈的非线性光学性质变化。这被解释为一种预活化，即界面水的局部有序度的增加，这有望促进表面冰的结晶。这一结果与最近在类似系统上进行的分子动力学模拟的预测一致。
We present and characterize a novel setup to apply second harmonic generation (SHG) spectroscopy in total internal reflection geometry (TIR) to heterogeneous freezing research. It allows to monitor the evolution of water structuring at solid surfaces at low temperatures prior to heterogeneous ice nucleation. Apart from the possibility of investigating temperature dependence, a major novelty in our setup is the ability of measuring sheet-like samples in TIR geometry in a direct way. As a main experimental result, we find that our method can discriminate between good and poor ice nucleating surfaces. While at the sapphire basal plane, which is known to be a poor ice nucleator, no structural rearrangement of the water molecules is found prior to freezing, the basal plane surface of mica, an analogue to ice active mineral dust surfaces, exhibits a strong change in the nonlinear optical properties at temperatures well above the freezing transition. This is interpreted as a pre-activation, i.e. an increase in the local ordering of the interfacial water which is expected to facilitate the crystallization of ice at the surface. The results are in line with recent predictions by molecular dynamics simulations on a similar system.