二价乙烷分子离子三体碎裂的解离机制研究  

Dissociation mechanism of ethane dication via three-body fragmentation

作　　者：张紫琪 闫顺成[1,2] 陶琛玉 余璇 张少锋 马新文[1,2] ZHANG Ziqi;YAN Shuncheng;TAO Chenyu;YU Xuan;ZHANG Shaofeng;MA Xinwen(Institute of Modern Physics,Chinese Academy of Sciences,Lanzhou 730000,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院近代物理研究所,兰州730000 [2]中国科学院大学,北京100049

出　　处：《物理学报》2025年第6期42-49,共8页Acta Physica Sinica

基　　金：国家重点研发计划(批准号:2022YFA1602500);中国科学院战略性先导科技专项(B)(批准号:XDB34020000);中国科学院“西部青年学者”项目资助的课题.

摘　　要：分子离子广泛存在于行星大气的电离层中,其碎裂可以产生多个离子和中性碎片.研究末态产物的动能分布和生成机理,可以促进理解行星大气的逃逸等天文现象.本文开展了电子碰撞乙烷的双电离碎裂实验,重点研究了C_(2)H_(6)^(2+)离子C—C键断裂后形成CH_(3)^(+)/CH_(2)^(+)/H的三体解离通道.直接测量了CH_(3)^(+)和CH_(2)^(+)离子的三维动量,然后利用动量守恒重构了H的动量.通过动能释放谱、Dalitz图、牛顿图分析了三体碎裂的解离机制.发现协同解离是产生该通道的主要机制,另有部分次序解离的贡献,其第一步是C_(2)H_(6)^(2+)解离生成H和亚稳态C_(2)H_(5)^(2+)第二步是C_(2)H_(5)^(2+)碎裂生成CH_(3)^(+)和CH_(2)^(+).实验发现H原子动能分布较广,最高能量甚至达到10 eV,远高于土卫六大气的逃逸能量,因而该解离路径对H逃逸过程有贡献.Molecular ions are widely distributed in the ionosphere of planetary atmospheres,and their fragmentations can generate different ions and neutral fragments.Studying the kinetic energy distribution and generation mechanism of the final products is helpful in understanding fundamental phenomena in astrophysics and plasma physics.In particular,ethane is an important molecule found in Titan and comet,and its fragmentation may be involved in the generation of complex hydrocarbons,as well as the atmospheric escape processes on Titan.In this paper,the experiment on ethane fragmentation by electron impact is carried out,focusing on the three-body fragmentation channel from C_(2)H_(6)^(2+)to CH_(3)^(+)to CH_(2)^(+)/H.The three-dimensional momenta of CH_(3)^(+)and CH_(2)^(+)ions are measured,and then the momentum of the H atom is reconstructed using momentum conservation law.Based on these analyses,the kinetic energy release(KER)spectrum and the fragmentation mechanisms are investigated.The time-of-flight(TOF)coincidence map of the ions shows two channels:channel(1)that represents the two-body dissociation generating CH_(3)^(+)/CH_(3)^(+),and channel(2)that refers to the three-body dissociation generating CH_(3)^(+)/CH_(2)^(+)/H.It is found that the neutral H from channel(2)has a wide kinetic energy distribution,ranging from 0 eV to more than 10 eV.This feature indicates that the dissociation of the C-H bond is from multiple electronic states.Since the escape threshold of H in Titan’s ionosphere is 0.02 eV,the vast majority of the H atoms produced in channel(2)can escape into outer space.In addition,the kinetic energy sum of CH_(3)^(+)and CH_(2)^(+)in channel(2)is found to be similar to the KER of channel(1),indicating that the C-H dissociation presents limited influence on the energy sum of the CH_(2)^(+)and CH_(3)^(+).The corresponding fragmentation mechanism of channel(2)is also analyzed in this work.the overall KER spectrum is divided into three parts:0–6 eV,6–9 eV,and 9–11 eV,and the respective Dalitz plots an

关 键 词：乙烷 电离解离 三体碎裂 反应显微成像谱仪 

分 类 号：O56[理学—原子与分子物理]