240—250nm波段氯苯的共振增强多光子电离研究

Study on Resonant Enhanced Multiphoton Ionazation of Chlorobenzene in the Range 240—250nm

首次报道了在超声分子束条件下,氯苯分子(C6H5Cl)在240-250nm紫外激发波段的共振增强多光子电离/飞行时间质谱(REMPI-TOFMS)。实验获得母体离子(112C6H5Cl+)和一些主要碎片离子的分质量光谱,以及它们在240.5nm和248.6nm两种激发波长下的光强指数。文中对母体离子及主要碎片离子的生成机理进行了探讨,研究表明:该波段范围内,氯苯分子首先吸收一个光子从基态1A1(S0)跃迁至激发态1B2(S1),激发态分子再吸收一个光子而电离,产生母体离子112C6H5Cl+;母体离子直接解离而生成碎片离子77C6H5+。质量更小的碎片离子51C4H3+和27C2H3+则是母体离子进一步吸收光子,然后通过快速的内转换而形成。在该波段范围内,氯苯的最佳检测波长为248.6nm。在该激发波长下,氯苯的探测限能达到到ppb量级。

The mass-resolved excited spectra for parent ion and the primary fragmentation ions were firstly obtained by using the resonant-enhanced multiphoton ionization（REMPI）of chlorobenzene in the range of 240—250nm.The dynamic yielding of parent ion and these primary daughter ions were discussed based on the mass-selected spectra and the laser power index of these ions at 240.5nm and 248.6nm and in different laser intensity.It is shown that chlorobenzene molecules firstly absorb one-photon and resonantly excite from ^1A1（S0）to ^1B2（S1）and then absorb another photon to produce ^112C6H5Cl^＋.^77C6H5＋^ was produced by the dissociation of parent ion ^112C6H5Cl^＋.^51C4H3＋^ and ^27C2H3＋^ were produced by ionization and dissociation of parent ion ^112C6H5Cl^＋.The measurement shows that 248.6nm is the suitable wavelength for ionization of chlorobenzene in this wavelength range.The detection limit of chlorobenzene is ppb level.