THE ZERO-KINETIC-ENERGY PHOTOELECTRON-SPECTRUM OF NITROGEN BETWEEN 15.5 AND 26.5 EV

The zero-kinetic-energy (ZEKE) photoelectron spectrum of nitrogen has been measured between 15.5 and 26.5 eV using synchrotron radiation at a resolution up to 5 meV. The rotational contours obtained, for the va rious vibrational components of the X2SIGMA(g)+(v+ = 0 -2) <-- X1SIGMA (g)+(v = 0) transitions are in good agreement with the results obtaine d using extreme ultraviolet (XUV) laser sources [Merkt and Softley, Ph ys. Rev. A 46, 302 (1992)], and appear to be strongly perturbed by aut oionization. The X and A states of the ion are observed up to v+ = 5 a nd 9, respectively, and the non-Franck-Condon intensity distribution o f these PrOgressions originates in part from autoionization of Rydberg states belonging to the series converging to the A and B states of th e ion. In contrast, the intensities of the v+ = 0, 1 components of the B state correspond well to Franck-Condon factors between neutral and ionic species. In addition, the rotational contour obtained for the B( v+ = 0) state is found to be identical to that measured by He i photoe lectron spectroscopy (PES) by Baltzer et al [Phys. Rev. A 46, 315 (199 2)]. Autoionization does therefore not seem to be a significant source of intensity in this region. The ZEKE spectrum between 23 and 26.5 eV shows considerably more structure than expected on the basis of previ ous lower resolution photoelectron spectroscopic studies and reveals a number of differences compared to a recent high-resolution He ii phot oelectron spectrum [Baltzer et al., Phys. Rev. A 46, 5545 (1992)]. At least three vibrational progressions are observed. The dominant one is attributed to the C state. Possible assignments for the other two pro gressions are discussed.