DETERMINATION OF THE IONIZATION-POTENTIALS OF ALUMINUM-OXIDES VIA CHARGE-TRANSFER

The ionization potentials of aluminum oxides (AlxOy) with x = 2, y = 1-4; x = 3, y = 2-4; and x = 4, y = 4 were determined to within 0.2 eV by charge-transfer bracketing measurements in a Fourier transform ion cyclotron resonance (ICR) mass spectrometer (FTMS). The method of determining the ionization potentials (IPs) of molecules by charge-transfer bracketing is extended from species produced by direct laser vaporization to species formed by reactions within the ICR cell. The IPs of aluminum oxides containing two aluminum atoms (Al2Oy) increase from 8.35 to 8.9 eV for y = 1-3. Upon addition of a fourth oxygen the IP decreases by approximately 2 eV, indicating a possible structural change from linear to cyclic. Aluminum oxides containing three aluminum atoms (Al3Oy) have IPs of 6.85 eV for y = 2 and 3. A dramatic increase in IP of 1.5 eV is observed upon addition of a fourth oxygen atom. The changes in IP are related to the oxidation state of the aluminum in the oxide species.