Theoretical method to evaluate photoionization spectra of small molecules in their excited states. Application to CH and N₂ molecules

Photoionization (PI) spectrum of the CH molecule is evaluated theoretically and compared with available experimental data for photon energies above the photoionization threshold at 12~eV. Vibrational motion and the vibronic coupling between the lowest vibrational and electronic states of CH and CH⁺ are accounted for in the present study. The multi-channel quantum defect theory with the vibrational frame transformation was employed in modeling the PI cross section of CH. The PI cross section is calculated for several initial vibrational levels of CH. A good agreement with the experiment by Gans et al. J. Chem. Phys. 144, 10.1063/1.4950880 (2016) for positions of observed resonances and the intensities of the resonances is found. Preliminary results for the N₂ molecule will also be presented.