The excited states of dimethyl siloxane and its dissociation products

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～1A1,and the three of lower-lying 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 CH4H2C2H6 in dissociation products,the is the same as the experimental[1].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[3].