Abstract: A density functional method(B3P86) with 6-31++g**(3df,3pd) basis sets has been used to study the geometric parameters, total energies, electronic structure and energy levels with the external electric field (－0.05~0.05 a.u.) along the y-and z-axe direction; On the basis of optimized configuration, the excitation properties of molecules are calculated by the configuration interaction singles(CIS-B3P86) method with external electric field. The results show that thegeometric parameters of molecules change obviously with the electric field. Such asexternal electric field in zdirection makes the bond length and dipole moment decrease, the total energy first decreases and then increases, and the energy gap decreases. The excitation energy and wavelength of the excited state change obviously with the size and direction of the external electric field, and the oscillator strength is affected by the direction of the electric field, which changes the transition performance of the molecule.

Key words: external electric field, excited states, oscillator strength