甲胺水合离子团簇的结构模型及红外光谱研究

本文利用量子化学计算方法，研究了甲胺和水复合离子团簇(CH₃NH₂)(H₂O)_n]⁺的几何结构、能量和红外光谱，揭示了结构生长模型、氢键作用机制和质子转移机理. 研究结果表明，在(CH₃NH₂)(H₂O)_n]⁺团簇中，甲胺甲基上的一个氢原子转移到氨基上，形成分子内质子转移的CH₂NH₃⁺离子核心结构模型，水分子作为氢键受体，与质子化氨基NH₃⁺形成氢键. CH₃NH₂⁺离子核心结构模型没有CH₂NH₃⁺离子核心结构模型稳定. 在团簇的红外光谱中，CH振动、自由NH振动、氢键结合的NH振动和OH振动模式在CH₃NH₂⁺和CH₂NH₃⁺两种离子核心结构模型的理论计算红外光谱中明显不同，因此可用于鉴别甲胺水合离子团簇的结构模型，有助于理解甲胺和水复合团簇的氢键网络结构.

Structures, Energetics, and Infrared Spectra of the Cationic Monomethylamine-Water Clusters

The structures, energetics, and infrared (IR) spectra of the cationic monomethylamine-water clusters, (CH₃NH₂)(H₂O)_n]⁺ (n=1-5), have been studied using quantum chemical calculations at the MP2/6-311+G(2d,p) level. The results reveal that the formation of proton-transferred CH₂NH₃⁺ ion core structure is preferred via the intramolecular proton transfer from the methyl group to the nitrogen atom and the water molecules act as the acceptor for the O????HN hydrogen bonds with the positively charged NH₃⁺ moiety of CH₂NH₃⁺, whose motif is retained in the larger clusters. The CH₃NH₂⁺ ion core structure is predicted to be less energetically favorable. Vibrational frequencies of CH stretches, hydrogen-bonded and free NH stretches, and hydrogen-bonded OH stretches in the calculated IR spectra of the CH₂NH₃⁺ and CH₃NH₂⁺ type structures are different from each other, which would afford the sensitive probes for fundamental understanding of hydrogen bonding networks generated from the radiation-induced chemical processes in the (CH₃NH₂)(H₂O)_n]⁺ complexes.