Photoelectron spectra from some autoionizing states of O2 near the ionization threshold

Abstract

The photoionization efficiency curve of O₂ and the vibrational distributions of photoelectrons from seven autoionizing states in the region of 0 ∼ 1.40 eV above threshold have been obtained. The apparatus used was composed of a vacuum ultraviolet monochromator, a quadrupole mass spectrometer, and a retarding‐field electron‐energy analyzer. The vibrational distributions of photoelectrons from autoionizing states were clearly different from those of calculated Franck‐Condon factors for the direct ionizing transition. The classification of the autoionizing states in this region is incomplete as yet; thus, that of Price and Collins was employed in calculation of Franck‐Condon factors for the autoionizing transitions. By comparison of the observations with the calculations the optimum values of internuclear spacing, r_e of the H, H′, and M progressions were determined to be 1.33 ± 0.01, 1.32 ± 0.01, and 1.28 ± 0.01 Å, respectively. The r_e value of the M progression significantly deviated from the calculated value using the empirical relation of $r_e^n{\omega }_e=\mathrm{const}$ . This deviation and the results of more detailed comparison of the observations with the calculations presented the problem of the classification of the autoionizing states especially in the case of the M progression.