Photoionization of N2 X 1Σ+g, v″=0 and 1 near threshold. Preionization of the Worley–Jenkins Rydberg series

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Abstract
The high resolution relative photoionization cross section for N2 is reported in the wavelength region from the ionization threshold to 650 Å, with particular attention given to the region between the N+2 X 2Σ+g, v′=0 and 1 ionization limits. Cross sections from both the X 1Σ+g, v″=0 and 1 vibrational levels were determined in this region, and preionized members of the npπu 1Πu Worley–Jenkins Rydberg series converging to N+2 X 2Σ+g, v′=1 are observed in both spectra. In the spectrum excited from v″=1, the Worley–Jenkins series appears prominently as a result of good Franck–Condon overlap between the N2 X 1Σ+g, v″=1 and the N+2 X 2Σ+g, v′=1 levels; the intensities of the series members decrease approximately as 1/n*3, in accord with simple theoretical predictions. However, in the spectrum excited from v″=0, the Worley–Jenkins series converging to N+2 X 2Σ+g, v′=1 is weak as a result of a poor Franck–Condon overlap with the ground vibrational level; the intensities of the series members show large deviations from the simple theory as a result of channel interactions with Rydberg states converging to N+2 A 2Πu. These perturbing Rydberg states have low photoabsorption oscillator strengths for excitation from v″=1 (in contrast to excitation from v″=0) and hence have only a small effect on the cross section from the excited vibrational level. Just as in the case of photoionization of H2, the results demonstrate that channel interaction can redistribute the oscillator strength of a perturbing Rydberg state of low principal quantum number over a number of members of an interacting Rydberg series and that the spectral range affected by the perturber can be much greater than the width of the perturbing level.