Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, USA.
J Am Chem Soc. 2011 Dec 14;133(49):19889-99. doi: 10.1021/ja208024p. Epub 2011 Nov 15.
Water cluster anions, (H(2)O)(N)(-), are examined using mixed quantum/classical molecular dynamics based on a one-electron pseudopotential model that incorporates many-body polarization and predicts vertical electron detachment energies (VDEs) with an accuracy of ~0.1 eV. By varying the initial conditions under which the clusters are formed, we are able to identify four distinct isomer types that exhibit different size-dependent VDEs. On the basis of a strong correlation between the electron's radius of gyration and its optical absorption maximum, and extrapolating to the bulk limit (N → ∞), our analysis supports the assignment of the "isomer Ib" data series, observed in photoelectron spectra of very cold clusters, as arising from cavity-bound (H(2)O)(N)(-) cluster isomers. The "isomer I" data reported in warmer experiments are assigned to surface-bound isomers in smaller clusters, transitioning to partially embedded isomers in larger clusters. The partially embedded isomers are characterized by a partially formed solvent cavity at the cluster surface, and they are spectroscopically quite similar to internalized cavity isomers. These assignments are consistent with various experimental data, and our theoretical characterization of these isomers sheds new light on a long-standing assignment problem.
水合簇负离子，(H(2)O)(N)(-)，使用基于单电子赝势模型的混合量子/经典分子动力学进行研究，该模型包含多体极化，并以约 0.1 eV 的精度预测垂直电子离解能 (VDE)。通过改变形成团簇的初始条件，我们能够识别出四种具有不同尺寸依赖性 VDE 的不同异构体类型。基于电子回转半径与其光吸收最大值之间的强相关性，并外推到体相极限 (N → ∞)，我们的分析支持将在非常冷的团簇的光电子能谱中观察到的“异构体 Ib”数据系列归因于空腔束缚 (H(2)O)(N)(-)团簇异构体。在较暖实验中报告的“异构体 I”数据被分配给较小团簇的表面结合异构体，在较大团簇中过渡到部分嵌入的异构体。部分嵌入的异构体的特征是在团簇表面部分形成溶剂空腔，并且它们在光谱上与内化空腔异构体非常相似。这些分配与各种实验数据一致，我们对这些异构体的理论表征为长期存在的分配问题提供了新的视角。
