High temperature photoelectron spectroscopy: Al2O and Al

The vapour phase HeI photoelectron spectra of Al2O and Al have been recorded using a new multidetector, high temperature photoelectron spectrometer. Ab initio molecular orbital calculations which include the effects of electron correlation show that the ground electronic state of Al2O has a D ∞h equilibrium geometry and, as a result, the four observed photoelectron bands are assigned to ionization from the outermost 5σ u , 6σ g , 2π u and 4σ u molecular orbitals. For atomic aluminium, three bands have been recorded and measurement of their relative intensities allows the Al 3s : 3p photoionization cross-section ratio to be measured as (0·36 ± 0·04) : 1 at the HeI photon energy. This result has proved useful in interpreting the relative band intensities in the Al2O spectrum.