Transition probabilities at threshold for the photoionization of molecular nitrogen

The relative transition probabilities at threshold for the photoemission of molecular nitrogen to vibrational levels of the X (2Σ+g), A (2Πu), and B (2Σ+u) states of the N+2 ion have been determined with high resolution threshold photoelectron spectroscopy using synchrotron radiation. These threshold cross sections are found to be strongly influenced by ionizing Rydberg states which are not necessarily apparent in the absorption or photoion spectrum of nitrogen. This interaction leads in the X (2Σ+g) state of N+2 to rotationlike structure in the observed vibrational transitions and in the A (2Πu) state to a smooth but non-Franck–Condon distribution of vibrational intensities. In addition to the cross section data, the molecular parameters for the X, A, and B states of N2 have been determined.