Suhara Ken-ichiro, Fujii Asuka, Mizuse Kenta, Mikami Naohiko, Kuo Jer-Lai
Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan.
J Chem Phys. 2007 May 21;126(19):194306. doi: 10.1063/1.2734969.
Infrared spectra of large-sized protonated methanol-water mixed clusters, H(+)(MeOH)(m)(H(2)O)(n) (m=1-4, n=4-22), were measured in the OH stretch region. The free OH stretch bands of the water moiety converged to a single peak due to the three-coordinated sites at the sizes of m+n=21, which is the magic number of the protonated water cluster. This is a spectroscopic signature for the formation of the three-dimensional cage structure in the mixed cluster, and it demonstrates the compatibility of a small number of methanol molecules with water in the hydrogen-bonded cage formation. Density functional theory calculations were carried out to examine the relative stability and structures of selected isomers of the mixed clusters. The calculation results supported the microscopic compatibility of methanol and water in the hydrogen-bonded cage development. The authors also found that in the magic number clusters, the surface protonated sites are energetically favored over their internal counterparts and the excess proton prefers to take the form of H(3)O(+) despite the fact that the proton affinity of methanol is greater than that of water.
在OH伸缩振动区域测量了大尺寸质子化甲醇 - 水混合团簇H⁺(MeOH)ₘ(H₂O)ₙ（m = 1 - 4，n = 4 - 22）的红外光谱。由于在m + n = 21尺寸时的三配位位点，水部分的自由OH伸缩振动带汇聚成一个单峰，这是质子化水团簇的幻数。这是混合团簇中三维笼状结构形成的光谱特征，它证明了少量甲醇分子与水在氢键笼状结构形成中的兼容性。进行了密度泛函理论计算以研究混合团簇选定异构体的相对稳定性和结构。计算结果支持了甲醇和水在氢键笼状结构发展中的微观兼容性。作者还发现，在幻数团簇中，表面质子化位点在能量上比其内部对应位点更有利，并且尽管甲醇的质子亲和力大于水，但过量质子更倾向于以H₃O⁺的形式存在。
