The outermost, singly ionized valence state of ${\mathrm{N}}_2$, the $X{}^2\Sigma _g^{+}$ state, is investigated in detail as a function of the photon frequency bandwidth for core excitation to the $\mathrm{N}1s\to {\pi }^{*}$ 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 $\mathrm{N}_2{}^{+}$ 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 $X{}^2\Sigma _g^{+}$ final state of $\mathrm{N}_2{}^{+}$.

• Received 15 April 2004

DOI:https://doi.org/10.1103/PhysRevA.70.032708