Kwon Sung, Sandhu Shawn, Shaik Moaid, Stamm Jacob, Sandhu Jesse, Das Rituparna, Hetherington Caitlin V, Levine Benjamin G, Dantus Marcos
Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States.
Department of Chemistry and Institute of Advanced Computational Science, Stony Brook University, Stony Brook, New York 11794, United States.
J Phys Chem A. 2023 Oct 19;127(41):8633-8638. doi: 10.1021/acs.jpca.3c05442. Epub 2023 Oct 9.
We examine the possibility that three hydrogen atoms in one plane of the cyclopropane dication come together in a concerted "ring-closing" mechanism to form H, a crucial cation in interstellar gas-phase chemistry. Ultrafast strong-field ionization followed by disruptive probing measurements indicates that the formation time of H is 249 ± 16 fs. This time scale is not consistent with a concerted mechanism, but rather a process that is preceded by ring opening. Measurements on propene, an isomer of cyclopropane, reveal the H formation time to be 225 ± 13 fs, a time scale similar to the H formation time in cyclopropane. Ab initio molecular dynamics simulations and the fact that both dications share a common potential energy surface support the ring-opening mechanism. The reaction mechanism following double ionization of cyclopropane involves ring opening, then H-migration, and roaming of a neutral H molecule, which then abstracts a proton to form H. These results further our understanding of complex interstellar chemical reactions and gas-phase reaction dynamics relevant to electron ionization mass spectrometry.
我们研究了环丙烷二价阳离子同一平面内的三个氢原子以协同“闭环”机制结合形成H⁺（星际气相化学中的一种关键阳离子）的可能性。超快强场电离后进行的破坏性探测测量表明，H⁺的形成时间为249±16飞秒。这个时间尺度与协同机制不一致，而是一个先开环的过程。对环丙烷的异构体丙烯进行的测量表明，H⁺的形成时间为225±13飞秒，这一时间尺度与环丙烷中H⁺的形成时间相似。从头算分子动力学模拟以及两种二价阳离子共享一个公共势能面这一事实支持了开环机制。环丙烷双电离后的反应机制包括开环，然后是H迁移，以及中性H分子的漫游，该中性H分子随后夺取一个质子形成H⁺。这些结果进一步加深了我们对与电子电离质谱相关的复杂星际化学反应和气相反应动力学的理解。
