离子速度成像方法研究溴代环己烷的紫外光解动力学

利用二维离子速度成像方法对C6H11Br分子在234 nm附近的光解动力学行为进行了研究. 通过(2+1)共振增强多光子电离探测了光解产物Br*(2P1/2)和Br(2P3/2), 得到它们的相对量子产率. 从光解产物Br*(2P1/2)和Br(2P3/2)的速度图像得到了能量和角度分布. 结果表明, Br*原子主要来自于S1态的直接解离, 而Br则绝大部分是从S2态向T3态的系间交叉跃迁得到, 并导致了两种解离通道能量分布的差别. 实验发现C6H11Br分子解离过程中大部分能量都转化为内能, 但与其它长链溴代烷烃分子相比, 可资用能更多地被分配到平动能中, 结合软反冲模型分析了这种能量分配跟环烷基的构象和稳定性的关系.

UV Photodissociation Dynamics of C6H11Br by Velocity Map Ion Imaging

The Photodissociation dynamics of C6H11Br was investigated near 234 nm. A two-dimensional photofragment ion-velocity imaging technique coupled with a (2+1) resonance-enhancedmultiphoton (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 relative quantum yields were obtained from (2+1) resonance-enhanced multiphoton ionization (REMPI) of the photofragment Br*(2P1/2) and Br(2P3/2). It was suggested that Br* came fromthe direct dissociation of S1 state mostly, while Br atom was produced by non-adiabatic transition between the S2 and T3 states. Consequently, the higher internal energy distribution and the broader translational energy distribution of Br channel than those of Br* formation channel can be explained well. The results indicated that a large fraction of the available energy translated into the internal energy of the fragments, which can be explained using the soft impulsive model. However, comparing with other long-chain bromoalkane, more available energy was translated into the kinetic energy. The relationship between the energy partition and the cyclohexyl radical structure were analyzed.