DOUBLY-CHARGED POSITIVE-IONS OF CHROMIUM HEXACARBONYL AND MOLYBDENUM HEXACARBONYL - CALCULATED AND MEASURED ELECTRONIC-STATE ENERGIES

Double-charge-transfer spectroscopy was used to measure the double-ion ization energies of chromium hexacarbonyl and molybdenum hexacarbonyl molecules to triplet electronic states of the corresponding dications. The spectra were interpreted using data calculated using a modified M SX alpha method. The measured double-ionization energy to the ground t riplet state is 22.8 +/- 0.5 eV for Cr(CO)(6) and 22.4 +/- 0.5 eV for Mo(CO)(6)(;) both values match, within experimental error, an earlier measurement of 22.8 +/- 0.5 eV for W(CO)(6). The spectra for the three hexacarbonyls are remarkably similar, probably reflecting that the el ectronic structures of the three molecules are almost identical in the valence region. The similarity is reflected in the calculated data; t he Coulomb repulsions between the two positive holes which characteriz e the dictations' states are 4.54, 4.44 and 4.45 eV for Cr(CO)(6)(2+), Mo(CO)(6)(2+) and W(CO)(6)(2+), respectively. These values correspond to the repulsive energy for two single charges separated by just over 3 Angstrom, this separation being consistent with the size of the mol ecules.