Photoionization Bands of Cyanogen: Multi-Mode Vibronic Coupling and Renner-Teller Effects

Multi-mode vibronic coupling in the X similar to 2 pi g ${{\tilde{X}}<^>{2}{\Pi }_{g}}$ , A similar to 2 sigma g+ ${{\tilde{A}}<^>{2}{\Sigma }_{g}<^>{+}}$ , B similar to 2 sigma u+ ${{\tilde{B}}<^>{2}{\Sigma }_{u}<^>{+}}$ and C similar to 2 pi u ${{\tilde{C}}<^>{2}{\Pi }_{u}}$ electronic states of Cyanogen radical cation (C 2 ${{}_{2}}$ N 2.+ ${{}_{2}<^>{.+}}$ ) is investigated with the aid of ab initio quantum chemistry and first principles quantum dynamics methods. The electronic degenerate states of pi symmetry of C 2 ${{}_{2}}$ N 2.+ ${{}_{2}<^>{.+}}$ undergo Renner-Teller (RT) splitting along degenerate vibrational modes of pi symmetry. The RT split components form symmetry allowed conical intersections with those from nearby RT split states or with non-degenerate electronic states of sigma symmetry. A parameterized vibronic Hamiltonian is constructed using standard vibronic coupling theory in a diabatic electronic basis and symmetry rules. The parameters of the Hamiltonian are derived from ab initio calculated adiabatic electronic energies. The vibronic spectrum is calculated, assigned and compared with the available experimental data. The impact of various electronic coupling on the vibronic structure of the spectrum is discussed.

Automated summary

This study investigates the multi-mode vibronic coupling in the X 2πg, A 2σg+, B 2σu+ and C 2πu electronic states of the Cyanogen radical cation (C2N2.+) using ab initio quantum chemistry and first principles quantum dynamics methods. The electronic degenerate states of pi symmetry of C2N2.+ undergo Renner-Teller splitting along degenerate vibrational modes of pi symmetry. A parameterized vibronic Hamiltonian is constructed using standard vibronic coupling theory and symmetry rules. The vibronic spectrum is calculated, assigned and compared with experimental data. The impact of different electronic couplings on the vibronic structure of the spectrum is discussed.