Wang Enliang, Ren Xueguang, Dorn Alexander
Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.
School of Physics, Xi'an Jiaotong University, Xi'an 710049, China.
Phys Rev Lett. 2021 Mar 12;126(10):103402. doi: 10.1103/PhysRevLett.126.103402.
Ionization and subsequent isomerization of organic molecules has been suggested as an important source of trihydrogen H_{3}^{+} cations in outer space. The high interest in such reactions has initiated many experimental and theoretical studies for various molecules. Here, we report measurements as well as ab initio molecular dynamics simulations on the fragmentation of dicationic methanol monomers and clusters ionized by low-energy (90 eV) electrons. Experimentally, for dicationic monomers, a fragmentation channel for the formation of H_{3}^{+} in coincidence with a COH^{+} cation is observed. The simulations show that an intermediate neutral H_{2} is formed in the first step, and its roaming around the dication ends in the formation of H_{3}^{+}. The entire reaction takes about 100-500 fs. The calculated kinetic energy release for the H_{3}^{+}+COH^{+} ion pair is in excellent agreement with the experimental result. In contrast, for the dicationic clusters, due to the possibility of distributing the two charges onto different molecules, several fast dissociation channels occur and suppress the roaming of H_{2} and formation of H_{3}^{+}. The present Letter suggests that the quenching of H_{3}^{+} formation by the chemical environment is a general phenomenon in dicationic clusters of organic molecules.
有机分子的电离及随后的异构化被认为是外层空间中三氢阳离子H₃⁺的重要来源。对这类反应的高度关注引发了针对各种分子的诸多实验和理论研究。在此，我们报告了关于低能（90电子伏特）电子电离的双电荷甲醇单体和团簇碎片化的测量结果以及从头算分子动力学模拟。在实验中，对于双电荷单体，观察到了一个与COH⁺阳离子同时形成H₃⁺的碎片化通道。模拟表明，第一步会形成一个中间中性H₂，它在双电荷周围的漫游最终形成H₃⁺。整个反应耗时约100 - 500飞秒。计算得到的H₃⁺ + COH⁺离子对的动能释放与实验结果高度吻合。相比之下，对于双电荷团簇，由于两个电荷可能分布在不同分子上，会出现几个快速解离通道，从而抑制了H₂的漫游和H₃⁺的形成。本快报表明，化学环境对H₃⁺形成的猝灭是有机分子双电荷团簇中的普遍现象。
