Photoelectron spectra of Ga20, In20 and Tl20

The HeI photoelectron spectra of Ga₂O, In₂O, and Tl₂O, as well as atomic In, have been obtained. Some spectral features of the recently published photoelectron spectrum of Al₂O differ noticeably from the heavier suboxides. The assignment of spectral features is supported by fully relativistic DVM SSC X_α calculations, which have been extended to include Al₂O. Best agreement is obtained between calculation and experiment for linear Al₂O, but for bent heavier metal suboxides. In general, the spectral features are indicative of ionic bonding, analogous to the behavior of group IIIB monohalides. Along the sequence Al₂O:Ga₂O:In₂O:Tl₂O, the highest occupied orbital becomes less and less localized on the metal atoms, with a rather dramatic decrease in metal character occurring at Tl₂O. The latter effect is attributable to a change in relative energies of the charge-adjusted metal and oxygen atomic orbitais and relativistic effects., A decrease in the relative ionization cross-section for molecular orbitais which have a large metal ns contribution is correlated with a similar behavior of the relative (ns)⁻¹cross-section for the corresponding atoms.