Bing Dan, Kuo Jer-Lai, Suhara Ken-ichiro, Fujii Asuka, Mikami Naohiko
School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore.
J Phys Chem A. 2009 Mar 19;113(11):2323-32. doi: 10.1021/jp900066u.
A surprising switch of the protonated site from methanol to water in protonated methanol-water mixed clusters, H(+)(MeOH)(m)(H(2)O)(1) (m = 1-9), was investigated by a joint theoretical and vibrational spectroscopic study. Extensive density functional calculations on all possible structural isomers revealed that the switch of the ion core is correlated with the size dependence and structural development of the hydrogen-bond network: (1) the CH(3)OH(2)(+) ion core is preferred for the small-sized clusters of m = 1 and 2, (2) coexistence of the H(3)O(+) and CH(3)OH(2)(+) ion cores is highly plausible for 3 < or = m < or = 7 clusters, and (3) obvious preference of the H(3)O(+) ion core appears from m > or = 8 with the appearance of the characteristic "tricyclic" structure of the hydrogen-bond network. The ion core switch at m approximately 8 is experimentally supported by the infrared photodissociation spectra of the size-selected clusters and the size dependence of the fragmentation channel following vibrational excitation.
通过理论与振动光谱联合研究，对质子化甲醇 - 水混合团簇H⁺(MeOH)ₘ(H₂O)₁（m = 1 - 9）中质子化位点从甲醇到水的惊人转变进行了研究。对所有可能的结构异构体进行的广泛密度泛函计算表明，离子核心的转变与氢键网络的尺寸依赖性和结构发展相关：(1) 对于m = 1和2的小尺寸团簇，CH₃OH₂⁺离子核心更受青睐；(2) 对于3 ≤ m ≤ 7的团簇，H₃O⁺和CH₃OH₂⁺离子核心共存的可能性很大；(3) 当m ≥ 8时，随着氢键网络特征性“三环”结构的出现，H₃O⁺离子核心明显更受青睐。m约为8时的离子核心转变得到了尺寸选择团簇的红外光解离光谱以及振动激发后碎片通道尺寸依赖性的实验支持。
