An ab initio diabatic study of rovibronic spectra of CN

An ab initio study of the rovibronic spectra for the cyano radical (CN) based on a diabatic representation is presented. This work considers 17 electronic states, 59 dipole moment curves, 88 spin-orbit coupling curves, and 30 electronic angular momentum coupling curves, which are obtained using the internally contracted multireference configuration interaction method including the Davidson correction (icMRCI + Q) with the aug-cc-pwCV5Z-DK basis set. The diabatic transformations are performed based on a property-based diabatization method to remove the avoided crossings for the D-2 Pi-H-2 Pi and b(4)Pi-2(4)Pi pairs. Ab initio potential energy curves of the X-2 Sigma(+), B-2 Sigma(+), E-2 Sigma(+), A(2)Pi, D-2 Pi, H-2 Pi, F-2 Delta and J(2)Delta electronic states are shifted to match the experimental electronic excitation energies and the equilibrium internuclear distances. The coupled nuclear motion Schr & ouml;dinger equations are then solved to obtain the rovibronic spectra of CN for wavenumbers from 0 to 80 000 cm(-1). At wavenumbers of 0-30 000 cm(-1), our absorption cross sections agree well with available theoretical data. For wavenumbers above 30 000 cm(-1), our cross sections are larger than previous data in view of the fact that the transitions involving high-lying electronic states are considered. This work provides an overall prediction of the rovibronic spectrum of CN. Our results are suitable for temperatures below 8000 K and could be useful for the investigations of planetary exploration.