光激发下的C_(60)

C_(60) EXCITED BY LIGHT

用电子一晶格耦合的紧束缚模型研究了光激发下的C_(60)分子。结果表明当电子由最高占据态激发到最低空态时,晶格发生弛豫,新激发态是环状双极化子,它有下述特点:键结构由基态时只有2种键长的二聚化变为有7种不同键长的层状,与基态相比,键长变化如环状极化子,赤道附近变化最大,二极处近乎不变;有2个能级进入能隙,成为自陷束缚态,它们定域在赤道附近;对称性由基态时I_h群降为D_(5d)群;预期会伴随出现非线性激子和4条核磁共振谱线。

Light-excited C_(60) is studied by electron-lattice coupling tight-binding model. When one or two electrons are excited from HOMO to LUMO, the lowest energy state is ring bipolaron with the following characteristics: (1) The bond structure is layers with seven different bonds. In comparison with the dimerized state, bond variation is like that of ring polaron: to be the largest in equator, nearly unchanged in poles. (2) Two energy levels get into the gap and form the self-trapping electronic bound states which localize in the equator area. (3) C_(60)'s symmetry reduces from I_h to D_(5d). (4) There exist nonlifiear exciton and 4 NMR lines.