A HE(I) PHOTOELECTRON SPECTROSCOPIC STUDY OF MGF2 IN THE GAS-PHASE

The He(I) photoelectron spectrum of gaseous magnesium difluoride, MgF2 , has been obtained by direct evaporation of a solid sample of MgF2 fr om a graphite furnace. The spectrum was obtained in the temperature ra nge 1770-2030 K and was found to consist of four overlapping bands wit h maxima at 13.8 5 +/- 0.02, 14.06 +/- 0.02, 14.34 +/- 0.02 and 14.96 +/- 0.01 eV. The first adiabatic ionization energy has been measured a s 13.41 +/- 0.05 eV in good agreement with an earlier value determined by electron impact mass spectrometry. Interpretation of the spectrum has been aided by calculation of vertical ionization energies using ab initio molecular orbital methods and the ionic state ordering is esta blished as 2PI(g), 2PI(u), 2SIGMA(u)+ and 2SIGMA(g)+ in order of incre asing ionization energy. The MgF2 spectrum is compared with photoelect ron spectra recorded previously for MgCl2 and MgBr2.