Gas phase and solid state X-ray photoelectron spectra of the substituted acetylenes (SF 5) n C 2 (CF 3) 2− n ( n = 0, 1, 2): A comparison of the pentafluorosulfur and trifluoromethyl groups

Abstract

The core level X-ray photoelectron spectra (XPS) of CF 3CCCF 3, CF 3CCSF 5 and SF 5CCSF 5 have been measured in the solid state. Gas phase spectra of CF 3CCCF 3 and CF 3CCSF 5 have also been obtained. The XPS data, interpreted with the point charge potential model and semiempirical MNDO (minimum neglect of differential overlap) molecular orbital calculations, indicate that the electron withdrawing effect of the −CF 3 group is greater than that of the −SF 5 group. Results further suggest that sulfur 3 d orbitals do not play a detectable role in the bonding or charge distribution in these molecules. Carbon 1 s linewidths of −CF 3 carbon atoms are found to be much narrower than those arising from the acetylenic carbon atoms. The narrower lines correlate with the much higher binding energy of the −CF 3 carbon atoms. Large shifts (nearly 1 eV) in heteroatom core level binding energy differences (for example, F 1 s — C 1 s) between the gas phase and solid state data are observed. These shifts are attributed to solid state effects (Madelung potential, intermolecular bonding interactions, and/or extramolecular relaxation contributions). From these comparisons it is clear that solid state effects are not uniform in their influence on the photoionized sites in these molecules.