Zurheide Florian, Dierking Christoph W, Pradzynski Christoph C, Forck Richard M, Flüggen Florian, Buck Udo, Zeuch Thomas
†Institut für Physikalische Chemie, Tammannstaße 6, Georg-August-Universität Göttingen, D-37077 Göttingen, Germany.
‡Max-Planck-Institut für Dynamik und Selbstorganisation, Am Faßberg 17, D-37077 Göttingen, Germany.
J Phys Chem A. 2015 Mar 19;119(11):2709-20. doi: 10.1021/jp509883m. Epub 2014 Dec 17.
In water clusters containing 10-100 water molecules the structural transition takes place between "all surface" structures without internally solvated water molecules to amorphous water clusters with a three dimensionally structured interior. This structural evolution is explored with rigorous size selection by IR excitation modulated photoionization spectroscopy of sodium-doped (H2O)n clusters. The emergence of fully coordinated interior water molecules is observed by an increased relative absorption from 3200 to 3400 cm(-1) in agreement with theoretical predictions and earlier experimental studies. The analysis has also shown that the intermediate-sized water clusters (n = 40-65) do not smoothly link the structures in the largest and smallest analyzed size regions (n = 15-35 and n = 100-150) in line with previous reports suggesting the appearance of exceptionally stable water cluster isomers at n = 51, 53, 55, and 57. In the size range from n = 49 to n = 55 a reduced ion yield, a plateau in the total IR signal gain and signatures in the distribution of free OH stretch oscillator absorption have been observed. Recently reported putative global minima structures for n = 51 and n = 54 point to the presence of periplanar interior rings in odd-numbered clusters in this size range, which may affect cluster (surface) stability and the shape of the free OH stretch absorption peak. Potential links between pure and sodium-doped water cluster structures and the signatures of solvated electrons in photoelectron spectra of anionic water clusters are discussed.
在含有10 - 100个水分子的水簇中，结构转变发生在没有内部溶剂化水分子的“全表面”结构与具有三维结构化内部的无定形水簇之间。通过对掺钠(H₂O)ₙ簇进行红外激发调制光电离光谱的严格尺寸选择来探索这种结构演变。通过3200至3400 cm⁻¹处相对吸收的增加，观察到了完全配位的内部水分子的出现，这与理论预测和早期实验研究一致。分析还表明，中等尺寸的水簇（n = 40 - 65）并没有平滑地连接最大和最小分析尺寸区域（n = 15 - 35和n = 100 - 150）中的结构，这与之前的报道一致，即表明在n = 51、53、55和57处出现了异常稳定的水簇异构体。在n = 49至n = 55的尺寸范围内，观察到离子产率降低、总红外信号增益出现平台以及自由OH伸缩振动吸收分布中的特征。最近报道的n = 51和n = 54的假定全局极小值结构表明，在这个尺寸范围内的奇数簇中存在近平面内部环，这可能会影响簇（表面）稳定性和自由OH伸缩吸收峰的形状。讨论了纯的和掺钠的水簇结构之间的潜在联系以及阴离子水簇光电子能谱中溶剂化电子的特征。
