Formation of highly vibrationally excited states of O+2 by threshold pulsed field ionization using coherent XUV

We report the observation of Franck—Condon forbidden highly vibrationally excited states of the oxygen molecular ion through threshold pulsed field ionization spectroscopy. The spectra were recorded using a broadly tunable coherent XUV light source for single-photon excitation of supersonically cooled oxygen. The rotational band contours are well described by the standard model for rotational linestrengths in photoelectron spectra, and are similar to those observed previously for Franck—Condon allowed bands.