碘代烷烃分子的C-I断键机理研究

C-I bond fission mechanism of alkyl iodides

利用离子速度成像方法对碘代直链烷烃和环烷烃分子在267 nm下的光解断键机理进行了研究.实验分析了激发态I~*(5p^2P_(1/2))和基态I(5p^2P_(3/2))的离子影像,得到其对应速度、角度分布的各向异性参数β值和相对量子产率Φ(I)和Φ(I~*)。实验发现碘代直链烷烃和环烷烃分子在吸收一个267nm的光子后,都发生快速的C-I断键,直接解离生成激发态I~*和基态I原子.与碘代直链烷烃相比,碘代环烷烃分子具有明显不同的角度分布特征,碘代环烷烃分子基态的β值大于激发态。并且随着α碳原子上所取代的烷基变重,φ(I~*)有变小的趋势。

The photodissociation mechanism of long-chain alkyl iodides and cyclic alkyl iodides at 267 nm were studied using ion velocity imaging technique. Speed and angular distributions of corresponding photofragments were obtained by detecting ion images of I^＊（5p2p1/2）. and I （5p2p.3/2）. Relative quantum yields Φ（I） and Φ（I＊） were also obtained. Iodine fragments in this study were both produced via direct and rapid dissociation of C-I bond after absorbing one photon of 267 nm. Compared to long-chain alkyl iodides, cyclic alkyl iodides have obviously different characteristics of angular distributions which the value of anisotropy parameter β for I is bigger than that for I＊. And as the alkyl group becomes heavier, Φ（I＊） tends to decrease.