关键词: 碘乙烷/
光解离/
离子速度成像/
飞行时间质谱
English Abstract
Multiphoton ionization dissociation dynamics of iodoethane studied with velocity map imaging technique
Yan Yi-Hui1,Liu Yu-Zhu1,2,
Ding Peng-Fei1,
Yin Wen-Yi1
1.Jiangsu Key Laboratory for Optoelectronic Detection of Atmosphere and Ocean, Nanjing University of Information Science and Technology, Nanjing 210044, China;
2.Jiangsu Collaborative Innovation Center on Atmospheric Environment and Equipment Technology, Nanjing 210044, China
Fund Project:Project supported by the National Key Research and Development Plan of China (Grant No. 2017YFC0212700), the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province of China (Grant No. 18KJA140002), and the State Key Laboratory for Artificial Microstructure and Mesoscopic Physics of Pecking University, China.Received Date:01 May 2018
Accepted Date:15 August 2018
Published Online:20 October 2019
Abstract:Halogenated alkanes destroy the ozone layer, and iodoethane is one of the important representative halogenated alkanes. Time-of-flight mass spectrometry and velocity map imaging technique are used for investigating the photoionization dissociation dynamics of iodoethane, induced by 800 nm femtosecond laser. The dissociation mechanisms of iodoethane are obtained and discussed by analyzing the velocity distributions and angular distributions of the fragment ions generated in the dissociation. The measurements by time-of-flight mass spectrometry show that iodoethane cations generates C2H5+, I+, CH2I+, C2H2+, C2H3+ and C2H4+. The fragments related to CI bond fragmentation are C2H5+ ions and I+ ions, and the dissociation mechanisms are C2H5I+ C2H5++I and C2H5I+ C2H5+I+ respectively. Comparison between the configurations before and after ionization shows that the CI bond length is 0.2220 nm before ionization and turns longer and becomes 0.2329 nm after ionization. This indicates that the CI bond becomes more unstable after ionization and is more prone to dissociation. Moreover, the velocity map images of C2H5+ and I+ ions are acquired, from which the speed and angular distribution of C2H5+ and I+ are obtained. The analysis of speed distribution of the fragment ions shows that there are two channels, i.e. high energy channel and low energy channel in the dissociation process for producing C2H5+ and I+ ion. The difference between the ratios of the high energy channel and the low energy channel is small, indicating that the high energy channel and the low energy channel of the two dissociation processes are similar. According to the further analysis of the angular distribution of the fragment ions, it is found that the anisotropy parameter of C2H5+ is close to 0 (isotropic), the production channel of which may correspond to the slow vibration predissociation process. The anisotropy parameters of I+ ions are higher, which may be due to the rapid dissociation process on the repulsive potential energy surface. In addition, the density functional theory is used to calculate the configuration change of the iodoethane molecule before and after ionization, the energy level and oscillator strength for the ionic state in order to obtain more insights into the photodissociation dynamics.
Keywords: iodoethane/
photodissociation/
velocity imaging/
time of flight mass spectrometry
