北京师范大学朱重钦团队报道了ClONO₂和HOCl在空气-水界面反应中自发生成Cl₂O的分子见解。相关研究成果于2023年7月31日发表于国际顶尖学术期刊《美国化学会杂志》。

平流层气溶胶表面的硝酸氯（ClONO₂）的化学过程对臭氧消耗至关重要。

该文中，研究人员展示了在空气-水界面的ClONO₂+HOCl反应中形成Cl₂O的反应路线，Cl₂O是平流层氯的来源。从头算分子动力学（AIMD）模拟表明，（ClONO2）Cl··O（HOCl）卤键在反应中起着关键作用，是ClONO₂和HOCl在空气-水界面和本体液态水中的主要相互作用。此外，基于元动力学的AIMD模拟揭示了两种途径：（i）HOCl的OCl片段与ClONO₂中的Cl原子结合，导致Cl₂O和NO₃^–的形成。同时，剩余的氢原子转移到水分子上形成H₃O⁺。（ii）HOCl充当Cl原子从ClONO₂转移到水分子的O原子的桥梁，该水分子将其一个H原子转移到另一个水分子，形成两个HOCl分子，NO₃^-和H₃O⁺。

自由能计算表明，前者是能量上更有利的过程。更重要的是，在空气-水界面形成Cl₂O的自由能垒仅为～0.8 kcal/mol，并且反应是放热的。

这些发现为基础氯化学的重要性以及气溶胶-空气-水界面对大气化学的更广泛影响提供了见解。

附：英文原文

Title: Molecular Insights into the Spontaneous Generation of Cl2O in the Reaction of ClONO2 and HOCl at the Air–Water Interface

Author: Zhengyi Wan, Chongqin Zhu, Joseph S. Francisco

Issue&Volume: July 31, 2023

Abstract: Chemical processes involving chlorine nitrate (ClONO2) at the surface of stratospheric aerosols are crucial to ozone depletion. Herein, we show a reaction route for the formation of Cl2O, which is a source of stratospheric chlorine, in the ClONO2 + HOCl reaction at the air–water interface. Our ab initio molecular dynamics (AIMD) simulations show that the (ClONO2)Cl···O(HOCl) halogen bond plays a key role in the reaction and is the main interaction between ClONO2 and HOCl both at the air–water interface and in the bulk liquid water. Furthermore, metadynamics-based AIMD simulations reveal two pathways: (i) The OCl fragment of HOCl binds to the Cl atom in ClONO2, resulting in the formation of Cl2O and NO3–. Simultaneously, the remaining hydrogen atom is transferred to a water molecule to form H3O+. (ii) HOCl acts as a bridge for Cl atom transfer from ClONO2 to the O atom of a water molecule, and this water molecule transfers one of its H atoms to another water molecule, forming two HOCl molecules, NO3–, and H3O+. Free-energy calculations show that the former is the energetically more favorable process. More importantly, the free-energy barrier for Cl2O formation at the air–water interface is only ～0.8 kcal/mol, and the reaction is exothermic. These findings provide insights into the importance of fundamental chlorine chemistry and the broader implications of the aerosol air–water interface for atmospheric chemistry.

DOI: 10.1021/jacs.3c06527

Source: https://pubs.acs.org/doi/10.1021/jacs.3c06527