Profile of resonant photoelectron spectra versus the spectral function width and photon frequency detuning

The outermost, singly ionized valence state of N₂, the X0.3em0ex²Σg⁺ state, is investigated in detail as a function of the photon frequency bandwidth for core excitation to the N0.3em0ex1s→π* resonance, where the photon frequency is tuned in between the first two vibrational levels of this bound intermediate electronic state. We find a strong, nontrivial dependence of the resulting resonant photoemission spectral profile on the monochromator function width and the frequency of its peak position. For narrow bandwidth excitation we observe a well resolved vibrational fine structure in the final electron spectrum, which for somewhat broader bandwidths gets smeared out into a continuous structure. For even broader monochromator bandwidths, it converts again into a well resolved vibrational progression. In addition, spectral features appearing below the adiabatic transition energy of the ground state of N₂⁺ are observed for broadband excitation. A model taking into account the interplay of the partial scattering cross section with the spectral function is presented and applied to the X0.3em0ex²Σg⁺ final state of N₂⁺.