Experimental evidence for high vibrational excitation in O-2(+) ground state by photoelectron spectroscopy

Photoelectron spectra of O-2 have been obtained using 584 angstrom photons produced in a helium discharge and 736-744 angstrom photons in a neon discharge. It is shown that the vibrational structure of O-2(+) (X-2 Pi g) ground state extends from 0-4 in the first case to 0-20 in the second one. The latter result cannot be explained on the basis of the Franck-Condon principle.