Crucial Role of Solvent-Impacted Molecular Anionic Resonances in Controlling Protonation Modes in the Acetonitrile鈥揥ater Anionic Cluster Revealed by ab Initio Molecular Dynamics Simulations

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• 作者：Shoushan Wang ; Jinxiang Liu ; Changzhe Zhang ; Li Guo ; Yuxiang Bu
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：October 2, 2014
• 年：2014
• 卷：118
• 期：39
• 页码：9212-9219
• 全文大小：450K
• ISSN：1520-5215

文摘

We present an ab initio molecular dynamics simulation study of a CH₃CN鈥?H₂O)₄₀ cluster with an excess electron (EE) injected vertically in this work. Instead of surface bound or internally solvated electron, a hydrated CH₃CN^{鈥?/sup> is first formed as the CN transient after geometrical relaxation. The driving forces for the formation of CH₃CN鈥?/sup> are bending vibration of 鈭燙CN angle, which initiates transfer of an extra charge to the CH₃CN LUMO, and hydration effect of the immediate water molecules, which plays a stabilizing role. Solvent thermal fluctuation can lead to different resonances (the quasi-C2-resonance versus quasi-N-resonance) from the CN transient and further cause the hydrated CH₃CN鈥?/sup> system to evolve via two distinctly different pathways featuring spontaneous proton transfer to the central C and N sites, producing two different protonation products, respectively. The solvent thermal fluctuation induced formation of hydrogen bonding with the corresponding sites (C2 versus N) is responsible for the quasi-resonances and interconversion between three resonant structures and further proton transfers featuring spontaneous transfer of a proton to C2 or to N from its interacting water molecule. The duration of CH₃CN鈥?/sup> for either of the two proton transfer processes is less than 200 fs. On the basis of experimental ESR results in which only the CH₃CHN radical was found and present theoretical calculations, it is suggested that the trans-CH₃CNH radical can be further converted to the CH₃CHN radical via a water-mediated hydrogen atom transfer path.}