Zhang Li-Min

Study on the Photodissociation Mechanism of N 2 O + via B 2 П i ← X 2 П Transitions

在超声分子束条件下，利用360．50nm的电离激光使N2O分子经由[3＋1]共振增强多光子电离（REMPI）产生纯净的N2O＋（X2∏（000））分子离子，用另一束解离激光在230—275nm范围扫描获得N2O^＋经由B2∏i←X^2∏跃迁产生的光解碎片（NO^＋和N2^＋）激发（PHOFEX）谱．获得的光解碎片激发谱可以归属为B2∏i（00n）←X^2∏（000）序列跃迁．我们分别将线性三原子分子离子N2^O＋中N—N伸缩振动简化成NO和N之间的简谐振动，N一0伸缩振动简化成N2和O之间的简谐振动，用谐振子的简谐势能曲线和波函数对N2O^＋分子离子X2∏和B^2∏i电子态振动能级间跃迁的Franck-Condon因子进行计算，和实验得到的碎片离子增强谱实验强度进行比较，对前人给出的分子数据（分子平衡核问距）进行验证，讨论了N2O^＋经由B^2∏i（00n）←X2∏（000）电子态跃迁的光解离机理和碎片离子的分支比．

An approach of estimating excitation cross sections in multiphoton processes

We suggest a simple approach to roughly estimate the excitation cross sections of various steps in a multiphoton ionization (or dissociation) process by applying the measured dependence of product signal on laser intensity. The validity of this method is demonstrated theoretically by means of the rate equations based upon a two-step kinetic model and can, in principle, be extended to the multiphoton process with steps more than two. Some results of numerical test and experiment are quoted.

GAS DYNAMIC PROBLEMS CAUSED BY THE GENERATION OF THE RADICALS IN A SUPERSONIC JET

A simplified one-dimensional model was proposed to treat the gas dynamic problems in a supersonic jet, which was used to produce radicals cooled by supersonic expansion. Based on this model, the gas dynamic equations can be integrated directly to obtain the evolution of the translational temperature and the rotational temperature of free radicals as well as the molecule density. The results show that the heating position where the radicals are generated and the initial rotational temperature of radicals have little effect on the rotational temperature at the down stream detection point, if the heating position is close to the nozzle orifice.