Empty levels in germanium compounds studied by XAS, ISEELS, ETS, DEAS and ab initio calculations: GeH4, GeCl4 and Ge(CH3)3Cl Original Research Article

The lower-lying empty levels of gaseous GeH4, GeCl4 and Ge(CH3)3Cl have been studied using X-ray absorption spectroscopy (XAS), inner shell electron energy loss spectrocopy (ISEELS), electron transmission spectroscopy (ETS), dissociative electron attachment spectroscopy (DEAS) and ab initio calculations. The inner shell excitation spectra include Ge 2p in GeH4, GeCl4 and Ge(CH3)3Cl; Ge 3s, Ge 3p and Cl 1s and Cl 2p in GeCl4. The Ge 2p and Cl 1s excitation spectra were obtained in gas phase at room temperature with a direct ion-yield technique at the LURE SUPER ACO storage ring in Orsay. The excitation spectra generated from p core orbitals are very sensitive to the change of ligand and geometry. Ab initio calculations employing the 1h-1p CI scheme performed for the Ge 1s, Ge 2s, Ge 2p absorptions for GeH4 and GeCl4 allow to assign and reproduce the main experimental below edge features whereas the composition of empty orbitals are deduced from the calculated oscillator strengths. The continuum above edge features reveal the presence of double excitations and shape resonances. Moreover complementary experimental results are reported for GeCl4. The Ge 3s, ge 3p and Cl 2p inner shell electrn energy loss spectra recorded under electric dipole scattering conditions give a complete picture of empty levels of different symmetries. Furthermore the ET spectrum (0–7 eV) of GeCl4 shows two resonance states located at 1.7 and 5.6 eV whereas the DEA spectrum is dominated by formation of the GeCl3− anion at zero impact energy and formation of Cl− and GeCl2− anions around 5.6 eV.