AB-INITIO CI CALCULATIONS OF THE CLS AND CL1S AND 2P CORE EXCITATION-SPECTRA OF THE FREON MOLECULES - CCL4, CFCL3, CF2CL2 AND CF3CL

Ab-initio calculations of the discrete C1s and C11s and 2p core excita tion 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, in dicating the reliability of the present computational approach to assi gn the spectral features. The interpretation of the final states in te rms of orbital composition, which is fuzzy in large molecules, is disc ussed in detail for the C1s spectrum of CF3Cl, as well as the variatio n of the spectrum induced by a change in the C-C1 bond length. The C1s calculated spectra show significant variations with the progressive s ubstitution of the chloride atom with the more electronegative fluorin e atom and are therefore a significant probe of the electronic structu re changes along the molecular series. The C11s and 2p results show a much less dependent behaviour of the spectra on the nature of the liga nd C1 or F attached to the C-atom, as expected since the C1 is in each case attached only to a C-atom, although variations are distinctly ap parent especially in the case of 2p spectra. (C) 1998 Elsevier Science B.V. All rights reserved.