【作者】 吴华；

【导师】 孙真荣；

【作者基本信息】 华东师范大学 ， 光学， 2015， 博士

【摘要】 超短超强脉冲激光的出现,使得原子和分子系统与强激光的相互作用出现了一系列新的现象,例如：高次谐波产生、多光子电离、场致电离、阈上电离、解离电离、场致解离、库仑爆炸等。卤代烷烃光解产生的卤素原子对臭氧层有极大的破坏作用,这使得卤代烷烃的光解问题成为化学动力学研究的热点。其中,溴原子对臭氧层的破坏作用更甚,为氯原子的100多倍,因此对于溴代烷烃光解动力学的研究具有极其重要的科学意义和应用价值。在本论文中,我们利用三维直流切片离子成像技术,研究了1,2-二溴乙烷分子、环己烷分子与飞秒激光相互作用发生解离电离和库仑爆炸的过程。具体研究工作如下：1.利用三维切片离子成像技术研究了1,2-C2H4Br2分子在800nm、80fs激光场中的库仑爆炸和解离电离过程。实验上测得了碎片离子C2H4Br+、Br+、C2H4+、Br2+和CH2Br+的切片图,计算获得了其动能分布和角分布参数。结果表明,相关离子的高动能分量来自于二价母体离子1,2-C2H4Br22+的库仑爆炸过程,低动能分量来自于一价母体离子1,2-C2H4Br2+的解离电离过程。在此基础上,理论模拟了产生离子C2H4+和Br2消除通道的反应路径,计算结果显示Br2分子的产生是异步协同消除反应,为一价母体离子同分异构化后越过势垒发生的解离。2.利用三维切片离子成像技术研究了在中心波长为800nm、脉冲宽度80fs的强场条件下,1,2-C2H4Br2分子发生协同消除反应产生碎片离子C2H4+和Br2+的通道。实验中随着光场强度的增长,解离过程越来越剧烈；当光场强度为增高到一定程度时,质谱上出现了质荷比m/q=156,158,160的新离子Br2+,这预示着新的库仑爆炸通道的出现。从头计算表明离子Br2+的产生为二价母体离子跨越0.18eV的势垒后发生的解离,为同步协同消除反应。光场强度达到1.0×1014W/cm2时离子Br2+的相对产率稳定在3.4%。3.利用三维切片离子成像技术研究了环己烷分子(C6H12)在800nm、80fs激光场中发生多光子解离和库仑爆炸的过程。实验上测得了不同光场强度下发生氢转移的离子CH3、C2H5+、C3H7+及其相关离子C5H9+、C4H7+、C3H5+的切片图,计算获得了各离子的速度分布和角分布参数。研究结果表明,离子的高动能分量来自于二价母体离子C6H122+的库仑爆炸过程,低动能分量来自于一价母体离子C6H12+的解离电离过程；CH3+、C2H5+、C3H7+离子的相对量子产率随着光场强度的升高分别趋于4.1%、2.6%、0.7%。最后,结合量子化学计算,研究了C6H122+发生库伦爆炸生成C2H4+和C4H8+的反应路径。更多还原

【Abstract】 With the advent of ultrafast intense laser, the interaction of atomic and molecular systems with intense laser field has attracted considerable attention in the past few decades. The corresponding phenomena, including of high-order harmonic generation, multi-photon ionization,field-assisted ionization, above threshold ionization, dissociative ionization, field-assisted dissociation, and Coulomb explosion, have been intensively and extensively investigated. The generated Br atom in the photodissociation process of hydrocarbon bromide have great damage to stratosphere ozone, where the catalytic rate of Br on depleting stratosphere ozone is100times more rapid than that of Cl. Thus the photoionization and photodissociation dynamics of hydrocarbon bromide in intense laser field has been an active field. In this thesis, we studied the dissociative ionization and Coulomb explosion processes of1,2-dibromoethane and cyclohexane molecules under an intense femtosecond laser field by dc-slice imaging technology. These specific works are presented as follows:1. Coulomb explosion and dissociative ionization of1,2-dibromoethane were experimentally investigated in near-infrared (800nm) femtosecond laser field by dc-slice imaging technology. The sliced images of these fragment ions C2H4Br+, Br+, C2H4+, Br2+and CH2Br+were obtained, and their corresponding kinetic energy releases (KER) and angular distributions were calculated. It was confirmed that the high-KER components come from Coulomb explosion of1,2-C2H4Br22+, while the low-KER components come from dissociative ionization of1,2-C2H4Br2+. Furthermore, the dissociation pathway leading to C2H4+and Br2was theoretically simulated, and the results showed that the singly charged precursor overcomes an energy barrier to dissociate via an asynchronous concerted mechanism after undergoing isomerization.2. Concerted elimination pathway leading to the fragment ions Br2+and C2H4+ from1,2-dibromoethane molecule has been investigated in800nm femtosecond laser field by dc-slice imaging technology. The kinetic energy release and angular distributions of Br2+and C2H4+demonstrated that Br2+resulted from the two-body Coulomb explosion of the doubly charged parent ion. Ab initio calculations showed that the doubly charged precursor overcome a small energy barrier (0.18eV) and then dissociated into Br2+and C2H4+through a synchronous concerted elimination mechanism. Moreover, the relative yield of the Br2+channel was obtained, and it remained about3.4%when the laser intensity exceeded1.0×1014W/cm2.3. The hydrogen migration pathways of cyclohexane in800nm femtosecond laser field have been investigated by dc-slice imaging technology. The observation of fragment ions CH3+, C2H5+and C3H7+could be regarded as the direct evidence that the chemical bond rearrangement processes associated with hydrogen migration occured in the dissociative ionization process of cyclohexane. The sliced images of fragment ions CH3+, C2H5+, C3H7+and their partner fragment ions C5H9+, C4H7+, C3H5+were obtained, and their corresponding kinetic energy release (KER) and angular distributions were calculated. It was confirmed that the high-KER components come from the two-body Coulomb explosion of C6H122+, while the low-KER components come from the dissociative ionization of C6H12+.Moreover, the relative yields of fragment ions CH3+, C2H5+and C3H7+were obtained, which approached to4.1%,2.6%and0.7%with the increase of the laser intensity, respectively. At last, the Coulomb explosion process of C6H122+into C2H4+and was studied with the aid of ab initio calculations.更多还原