对氯苯酚的共振增强多光子电离研究

Study on resonance enhanced multiphoton ionization of p-chlorophenol

在自行研制的具有恒温加热进样系统的激光质谱仪上实验研究了气相对氯苯酚分子的共振增强多光子电离飞行时间质谱(REMPI-TOFMS),获得了在275-285 nm激发波段的母体离子和主要碎片离子(C6H5O+,C5H5Cl+C6H5+,C5H5+,C4H3++,C3H3+)的(1+1)REMPI激发光谱。通过质谱光谱分析,结合分子在中间激发态的能级和结构特征,对主要碎片离子的形成机理进行了研究。结果显示:各个碎片离子与对氯苯酚的母体离子具有相似的光激发谱,并且各个谱峰与S1态的振动能级是一一对应的。说明各个碎片离子和母体离子的产生经历了相同的共振中间态。分子先吸收一个光子到达中间共振态,然后再吸收一个光子到达电离态电离。根据碎片离子光强指数的阶梯形分布和分子在S1态的结构特点,判断各个碎片离子经历了母体离子的阶梯式离解,并给出了主要碎片离子的离解通道。

The resonance enhanced multiphoton ionization/time-of-flight mass spectra of p-chlorophenol are studied by using a laser mass spectrometer with special designed heated sample inlet system. The REMPI excitation spectra （275-285 nm） of the parent ion （4-ClP^＋） and the fragment ions （C6H5O^＋, C5H5Cl^＋, C6H5^＋, C5H5^＋, C4H3^＋, C3H3^＋） are acquired. It was shown that the excitation spectra from different fragment ions or the parent ion are found to have the similar spectra features due to the same intermediate state. The chlorophenol molecular is firstly one photon resonantly excited to the intermediate state, and then absorbs another photon to produce the parent ion （C6H5O^＋）. In combination with the structure of p-chlorophenol in the S1 state and the power indexes of different fragment ions, the results indicate that fragment ions are produced from the parent ion through the ladder mechanism.