离子速度成像方法研究二溴甲烷的紫外光解动力学

利用二维离子速度成像(Ion-Velocity Imaging)方法对二溴甲烷分子在234和267 nm附近的光解动力学行为进行了研究. 实验中得到了二溴甲烷光解产生的Br^*(²P_1/2)和Br(²P_3/2)在不同波长下的角度和平动能分布. 在平动能分布中发现两个高斯分布, 推测其中主要是C—Br的快速解离, 而高能宽分布则来自于CH₂Br自由基的二次解离过程. 通过角度分布得到了Br^*与Br中来自直接解离和非绝热交叉跃迁两种来源的比例. 结果表明Br^*原子主要来自于B₁态的直接解离, 而Br则绝大部分是从B₁态向A₁的非绝热交叉跃迁得到, 并导致了两种解离通道能量分布的差别.

Photodissociation Dynamics Study of CH2Br2 in Ultraviolet Region by the Ion-Velocity Imaging Technique

The photodissociation dynamics of CH2Br2 was investigated near 234 and 267 nm. A two di- mensional photofragment ion-velocity imaging technique coupled with a (2 1) resonance-enhanced mul- tiphoton (REMPI) ionization scheme was utilized to obtain the angular and translational energy distributions of the nascent Br(2P3/2) and Br*(2P1/2) atoms. The translational energy distributions of Br and Br* were found to consist of two components which should come from the radical channel and secondary dissociation proc- ess, respectively. By analyzing the angular distributions, the fractions of the direct and non-adiabatic disso- ciation in the Br and Br* channels were obtained. It was suggested that Br* come from the direct dissociation of B1 state mostly, while Br atom be produced by non-adiabatic transition between the B1 and A1 states. Consequently, the phenomena of the higher internal energy distribution of Br channel than that of Br* for- mation channel and the broader translational energy distribution of the former can be explained well.