甲烷在外场作用下的光激发特性研究

Study on the effect of external electric field excitation on methane

采用密度泛函B3LYP和组态相互作用方法在6311++G水平上计算了甲烷从基态到前六个激发态的跃迁波长,振子强度,自发辐射系数An0和吸收系数B0n(n=1—6).同时研究了外电场对甲烷分子的激发态的影响规律.结果表明,随外电场强度增大,系统总能量变化较小,同时最高占据轨道HOMO与最低空轨道LUMO的能隙gaps变小,费米能级Fermilevels略有下降.甲烷基态(X～1A1)在外场作用下,易于向高激发态产生跃迁.

The present paper is devoted to the calculation of transition wavelengths, oscillator strengths f, Einstein A(n0) and B-0n, coefficients of methane from ground state X(1)A(1), to the first six different excited states by employing density functional theory and single substitute configuration interaction (CIS) approach with basis sets 6-311 + + G* *. At the same time, the excited states of methane under an external electric field are investigated. It is shown that the total energy of the system has little changed, and simultaneously the HOMO-LUMO gaps become small and the Fermi levels declines slightly as the external electric field intensity become strong. The transition between ground state X(1)A(1), and the high-excited state of methane is easy bring about.