• Chinese Journal of Chemical Physics
  • Vol. 33, Issue 5, 05000583 (2020)
Geng Lijun1、2, Zhang Hanyu2, Wu Haiming2, Sun Zhendong1、3、*, and Luo Zhixun2、*
Author Affiliations
  • 1School of Physics, Shandong University, Ji'nan 250100, China
  • 2Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
  • 3School of Physics and Electrical Engineering, Kashi University, Kashgar 844006, China
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    Abstract

    We report a study on photo-ionization of benzene and aniline with incidental subsequent dissociation by the customized reflection time-of-flight mass spectrometer utilizing a deep ultraviolet 177.3 nm laser. Highly efficient ionization of benzene is observed with a weak C$ _4 $H$ _3 $$ ^+ $ fragment formed by undergoing disproportional C$ - $C bond dissociation. In comparison, a major C$ _5 $H$ _6 $$ ^{+\cdot} $ fragment and a minor C$ _6 $H$ _6 $$ ^{+\cdot} $ radical are produced in the ionization of aniline pertaining to the removal of CNH$ ^\cdot $ and NH$ ^\cdot $ radicals, respectively. First-principles calculation is employed to reveal the photo-dissociation pathways of these two molecules having a structural difference of just an amino group. It is demonstrated that hydrogen atom transfer plays an important role in the cleavage of C$ - $C or C$ - $N bonds in benzene and aniline ions. This study is helpful to understand the underlying mechanisms of chemical bond fracture of benzene ring and related aromatic molecules.

    Ⅰ INTRODUCTION

    Photon-induced reactions play an important role in modern chemistry and enable researchers to elucidate elementary chemical processes in polyatomic molecules and ions [1], thereby in the past decades extensive efforts have been devoted to both experiments and theoretical studies for illustrating the reaction pathways of polyatomic molecules and cluster ions [1-5], among which the investigations of photo-induced ionization and dissociation mechanisms have attracted considerable interests via mass spectrometry [3-5]. Various ionization methods and mass spectrometry techniques have been developed in recent decades [6-10], which have been used by researchers for customization and personalization of components combined with the general mass spectrometric measurements for chemical identifications. In the ionization process, mass spectrometry in the gas phase can eliminate the uncertainties of ion signals and the contaminating agents and/or impurities from environment [6]. In particular, chemical structures can be determined from fragments analysis by assuming both the mass-to-charge ratio and the precursor/product composition being consistent with each other [11]. The availability of photo-ionization and photo-dissociation in mass spectrometry in identifying chemical structure had important applications in genomics and proteomics [12-14]. Recently, characterizing the photophysical and photochemical properties of small aromatic molecules of benzene (C$ _6 $H$ _6 $) and aniline (C$ _6 $H$ _7 $N), which are also the study samples of this work, has attracted increasing research interest [15, 16].

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    Lijun Geng, Hanyu Zhang, Haiming Wu, Zhendong Sun, Zhixun Luo. Ionization and Dissociation of Benzene and Aniline under Deep Ultraviolet Laser Irradiation[J]. Chinese Journal of Chemical Physics, 2020, 33(5): 583
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    Received: Jun. 5, 2020
    Accepted: Jul. 13, 2020
    Published Online: Apr. 21, 2021
    The Author Email: Sun Zhendong (zxluo@iccas.ac.cn), Luo Zhixun (zxluo@iccas.ac.cn)