韩国首尔基础科学研究院Ihee, Hyotcherl团队报道了分子离子的生成和结构转变的探测。相关研究成果发表在2024年1月10日出版的《自然》。

分子离子无处不在，并且在许多反应中发挥着关键作用，特别是在大气和星际化学的背景下。然而，由于实验困难，与中性分子相比，它们的结构和构象转变，特别是在气相中，很少被探索。一个很好的例子是卤鎓离子，其高反应性和环应变使它们成为短寿命的中间体，即使是弱亲核试剂也很容易攻击它们，因此在它们进行进一步反应之前很难分离或捕获。

该文中，研究人员表明，兆电子伏特超快电子衍射（MeV UED）与共振增强多光子电离结合使用，可以监测1，3-二溴丙烷（DBP）阳离子的形成及其随后形成卤离子的结构动力学。研究人员发现，DBP⁺阳离子在结构上与DBP电子基态无法区分的恰当命名的“暗态”中保留了3.6ps的相当长的持续时间。

由表面跳跃模拟和从头计算结构数据表明，阳离子随后衰变为异DBP⁺，这是一种不寻常的中间体，具有含有松散结合溴原子的四元环，最终失去溴原子，形成具有三元环结构的溴离子。研究认为这里使用的方法也可以应用于研究其他分子离子的结构动力学，从而加深人们对离子化学的理解。

附：英文原文

Title: Capturing the generation and structural transformations of molecular ions

Author: Heo, Jun, Kim, Doyeong, Segalina, Alekos, Ki, Hosung, Ahn, Doo-Sik, Lee, Seonggon, Kim, Jungmin, Cha, Yongjun, Lee, Kyung Won, Yang, Jie, Nunes, J. Pedro F., Wang, Xijie, Ihee, Hyotcherl

Issue&Volume: 2024-01-10

Abstract: Molecular ions are ubiquitous and play pivotal roles1,2,3 in many reactions, particularly in the context of atmospheric and interstellar chemistry4,5,6. However, their structures and conformational transitions7,8, particularly in the gas phase, are less explored than those of neutral molecules owing to experimental difficulties. A case in point is the halonium ions9,10,11, whose highly reactive nature and ring strain make them short-lived intermediates that are readily attacked even by weak nucleophiles and thus challenging to isolate or capture before they undergo further reaction. Here we show that mega-electronvolt ultrafast electron diffraction (MeV-UED)12,13,14, used in conjunction with resonance-enhanced multiphoton ionization, can monitor the formation of 1,3-dibromopropane (DBP) cations and their subsequent structural dynamics forming a halonium ion. We find that the DBP+ cation remains for a substantial duration of 3.6ps in aptly named ‘dark states’ that are structurally indistinguishable from the DBP electronic ground state. The structural data, supported by surface-hopping simulations15 and ab initio calculations16, reveal that the cation subsequently decays to iso-DBP+, an unusual intermediate with a four-membered ring containing a loosely bound17,18 bromine atom, and eventually loses the bromine atom and forms a bromonium ion with a three-membered-ring structure19. We anticipate that the approach used here can also be applied to examine the structural dynamics of other molecular ions and thereby deepen our understanding of ion chemistry.

DOI: 10.1038/s41586-023-06909-5

Source: https://www.nature.com/articles/s41586-023-06909-5