多光子电离伴随的碎片化过程的速率方程分析

提出一个描述多原子分子多光子激发、电离和离子再被激发过程的布局速率方程模型，并且得到电离效率和离子体系吸收的平均能量＜E＞的代数解．通过计算这两个量与光强的关系，分析了不同电离机制下，多原子分子多光子电离实验中伴随的碎片化过程的控制性问题．结果表明只有采用1＋1电离方案，可以通过控制电离激光的强度来实现“软电离”和“硬解离”．采用3＋1电离，即使在单离子条件下，离子的＜E＞已高达20－30eV，远超过离子的解离阈值，特别是增加光强时，＜E＞的增加速度比电离效率增加得快，因此一般条件下不能让分子有效电离而不使其离子解离．上面的分析可以圆满解释呋喃等分子在3＋1电离时观察不到母体离子这个实验事实．

Population Rate Equation Analysis of Controllability of Fragmentation Process in Multiphoton Ionization Experiments of Polyatomic Molecules

On the basis of population rate equation of multiphoton ionization and fragmentation processes, the colirollability of fragmentation process in MPI experiments ofpolyatomic molecules is analyzed in this paper. Curves of ionization efficiency and meanenergy < E > of ions versus laser intensity were calculated for different ionization schemes.From the calculation results, we find that only 1 1 ionization scheme, soft ioinzation andhard fragmntation can be controlled by changing the intensity of ionization laser. For3 1 ionizaton scheme, due to additional absorption photons after ionization, the ions havealready obtained internal energy about 20 ~ 30eV/per ion even at single ion detectionlimit. This amount of energy far exceeds the dissociation threshold of the parent ion, sothe parent ions formed by ionization can completely dissociate to daughters in the samelaser pules. Our analyses can explain why parent ions didn't appear in MPI mass spectraof furan molecule at 450nm.