二甲基硅酮的分子激发态和离解产物

The excited states of dimethyl siloxane and its dissociation products

用SAC-CI／6—311g方法计算了二甲基硅酮[DMS，（CH3）2SiO]的单重态和其激发态，得到基态为X^-1A1，其3个低激发态依次为^1A2、^1A1和^1B1，其电子光谱都出现在紫外可见区，这是二甲基硅酮（DMS）的独特之点。根据群的对称性原理，指出在二甲基硅酮[DMS，（CH3）2SiO]中（图1），同时离解5H和8H，是对称性最许可的。计算出同时离解3C-5H和4C-8H时的离解能和同时离解键1Si-3CH3和1Si-4CH3时的离解能，由基H和CH3会发生自由基反应，这与脉冲辐射的紫外可见光谱无结构的实验相合。可以预计在离解气体产物中，甲烷CH4成分最多，其次为H2，乙烷C2H6最少，文献[1]的实验正是如此。

The ground state and excited states of dimethyl siloxane [DMS, （CH3）2SiO] are calculated using method SAC-CI/6-311g, the ground state is X^-1 A1, and the three of lowerlying excited states are ^1A2, ^1A1 and ^1B1. The electronic spectrum of DMS is in ultraviolet-visible region. Follow the symmetry of group, the dissociation of the 5H and 8H （fig 1） in DMS are most possible. The dissociation energy for both bonds 3C-5H and 4C-8H, and for both bonds 1Si-3CH3 and 1Si-4CH3 are calculated, from which it is expected that the contents will be CH4〉 H2〉C2H6 in dissociation products , the is the same as the experimental. The most of intermediate are the free radicals H,CH3 etc then, produce H2, CH4 and C2H6 from free reactions, which is in agreement with the experimental.