Abstract: We independently developed a complete set of high-precision numerical model, in which diabatic theory has successfully been applied to study the high-resolution vibronic spectra of polyatomic molecules(n>5). We presented a new efficient approach for determining the vibrational frequencies at the conical intersection without trivial GF analysis in the former work. Also, the effective vibronic Hamiltonian has been investigated. Terms in the Hamiltonian up to any order at will are given explicitly by our recursive algorithm.

Key words: Diabatic model, Vibronic coupling, Cartesian, Harmonic oscillator, Raising and lowing operator