Ab-initio CI calculations of the C1s and Cl1s and 2p core excitation spectra of the freon molecules: CCl4, CFCl3, CF2Cl2 and CF3Cl Original Research Article

Ab-initio calculations of the discrete C1s and Cl1s and 2p core excitation spectra of the freon molecules CCl4, CFCl3, CF2Cl2 and CF3Cl are performed in the relaxed 1h–1p CI scheme. Satisfactory agreement with the experimental patterns is obtained for all the spectra analysed, indicating the reliability of the present computational approach to assign the spectral features. The interpretation of the final states in terms of orbital composition, which is fuzzy in large molecules, is discussed in detail for the C1s spectrum of CF3Cl, as well as the variation of the spectrum induced by a change in the C–Cl bond length. The C1s calculated spectra show significant variations with the progressive substitution of the chloride atom with the more electronegative fluorine atom and are therefore a significant probe of the electronic structure changes along the molecular series. The Cl1s and 2p results show a much less dependent behaviour of the spectra on the nature of the ligand Cl or F attached to the C-atom, as expected since the Cl is in each case attached only to a C-atom, although variations are distinctly apparent especially in the case of 2p spectra.