Observation of autoionization in O2 by an electron-electron coincidence method

A strong transition to an autoionizing stata has been observed in O2 at 16.83 ± 0.11 eV by means of a new electron-electron conincidence method. The method uses the fact that electrons arising from autoionizing states appear at a constant energy loss corresponding to the excitation energy of the autoionizing state rather than at a constant ionization potential as do electrons produced by direct ionization. Comparison of the present data with previous photoionization studies suggests that the autoionizing O2 state is the same state deduced to be responsible for abnormal vibrational intensities in the O2+X2Πg ground state when 16.85 eV Ne(I) photons are used. These electron-electron coincidence experiments provide a direct new method for the study of autoionization produced by electron impact.