VIBRATIONALLY RESOLVED THRESHOLD PHOTOEMISSION OF N2 AND CO AT THE N-K EDGE AND C-K EDGE

Zero-kinetic-energy photoelectron spectroscopy was used to measure the Franck-Condon factors for the carbon and nitrogen K-shell ionized states in N2 and CO. Corresponding features in the two spectra showed nearly identical energy spacings, both below and above the ionization threshold, as predicted by the equivalent-core model. The equilibrium bond length, R(e) for the CO C-1s-1 state was determined to be 1.077+/-0.005 angstrom, and R(e) for the N2 N-1s-1 state was found to be 1.077+/-0.010 angstrom, changes of -0.051 angstrom for CO and -0.020 angstrom for N2 from their ground-state equilibrium bond lengths. The two-electron states corresponding to 1s-1 val-1-pi* were examined in the binding energy region predicted by Green function calculations. Two-electron states absent in the X-ray photoemission spectrum are present in both molecules and show evidence of vibrational structure.