Matsuda Yoshiyuki, Mori Mayumi, Hachiya Masaki, Fujii Asuka, Mikami Naohiko
Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki-Aoba, Aoba-ku, Sendai 980-8578, Japan.
J Chem Phys. 2006 Oct 28;125(16):164320. doi: 10.1063/1.2360279.
Infrared predissociation spectroscopy of vacuum ultraviolet-pumped ion (IRPDS-VUV-PI) is performed on ammonia cluster cations (NH3)n+ (n=2-4) that are produced by VUV photoionization in supersonic jets. The structures of (NH3)2+ and (NH3)4+ are determined through the observation of infrared spectra and vibrational calculations based on ab initio calculations at the MP2/6-31G** and 6-31++G** levels. (NH3)2+ is found to be of the "hydrogen-transferred" form having the (H3N+-...NH2) composition. In contrast, (NH3)4+ exhibits the "head-to-head" dimer cation (H3...NH3+ core structure, where the positive charge is shared between two ammonia molecules in the core, and two other molecules are hydrogen bonded onto the core. An unequivocal assignment of the infrared spectrum of (NH3)3+ has not been achieved, because the presence of two isomeric structures could be suggested by the observed spectrum and theoretical calculations.
对在超声速射流中通过真空紫外光电离产生的氨簇阳离子(NH₃)ₙ⁺（n = 2 - 4）进行了真空紫外泵浦离子的红外预解离光谱（IRPDS - VUV - PI）研究。基于MP2/6 - 31G和6 - 31++G水平的从头算计算，通过红外光谱观察和振动计算确定了(NH₃)₂⁺和(NH₃)₄⁺的结构。发现(NH₃)₂⁺是具有(H₃N⁺ -...NH₂)组成的“氢转移”形式。相比之下，(NH₃)₄⁺表现出“头对头”二聚体阳离子(H₃...NH₃⁺核心结构，其中正电荷在核心中的两个氨分子之间共享，另外两个分子通过氢键连接到核心上。由于观察到的光谱和理论计算表明可能存在两种异构结构，因此尚未实现对(NH₃)₃⁺红外光谱的明确归属。
