摘要
本文采用脉冲分子束和飞行时间质谱技术研究在UV激光辐照下环氧乙烷多光子电离和解离过程,测得在308nm激光辐照下主要解离产物为HCO^+。CH^+和C_2H_3O^+.其光强指数分别为2.8,2.9和2.9.此外也观察到少量CH_2^+,CH_4^+,和H^+等产物离子.在355nm激光辐照下主要解离产物为HCO^+,CH_3^+,CH_2^+,CH^+和CH_3CO^+以及少量H^+和C^+等.对于HCO^+,CH_3^+,CH_2^+,CH^+和H^+离子,其光强指数依次为4.0,3.1,3.5,3.7和4.1.根据实验结果,对于环氧乙烷多光子电离和解离过程的机理作了讨论.
Multiphoton ionization and dissociation (MPID) of ethylene oxide molecule at 308nm and 355nm laser radiation are investigated using a pulsed molecular beam and time of flight mass spectrometric techniques. Three relative strong peaks assigned to HCO^+, CH_3^+ and C_2H_3O^+ and some week peaks assigned to CH_2^+, CH_4^+, H^+ etc. are observed from the MPID-TOF mass spectrum of ethylene oxide under 308nm laser irradiation. The dependence of the ion signal intensity on laser power is measured. The laser power dependence of HCO^+, CH_3^+, and C_2H_3O^+ are 2.8, 2.9 and 2.9, respectively. In the case at 355nm laser radiation, the major products of MPID of ethylene oxide are HCO^+, CH_3^+, CH_2^+, CH^+ and CH_3CO^+. In addition, some week peaks assigned to H^+, C^+are also observed. The laser power dependence of HCO^+, CH_3^+, CH_2^+, CH^+, and H^+ are 4.0, 3.1, 3.5, 3.7 and 4.1 respectively. According to these results,the mechenism of MPID process of ethylene oxide can be proposed as follows: firstly, the ethylene oxide is ionized by 3 and 4 photons absorption under 308nm and 355nm laser irradiation, respectively, then the excited ethylene oxide ion is isomerized to the acetaldehyde structure and immediately dissociated into the fragments.
