ACCURATE DENSITY-FUNCTIONAL CALCULATION OF CORE ELECTRON-BINDING ENERGIES .5. APPLICATION TO NITRILES - MODEL MOLECULES FOR POLYACRYLONITRILE REVISITED

A recent procedure for computing accurate core electron binding energi es (CEBEs) via density functional theory (DFT) is applied to acetonitr ile, propionitrile, 2-cyanopropane, acrylonitrile, methacrylonitrile a nd the 2-methylglutaronitrile conformer of lowest energy, The first th ree systems have been studied in the past as model compounds to interp ret the XPS spectrum of polyacrylonitrile (PAN) using post-Hartree-Foc k finite-difference calculations, in order to solve a controversy in t he assignment of chemically shifted atoms in the C 1s region, This ass ignment is revisited with the unrestricted generalized transition-stat e model and a combined functional of Becke's 1988 exchange with Perdew 's 1986 correlation. Using Dunning's correlation-consistent polarized valence triple zeta basis sets with scaling improvements, we obtain pr edicted CEBEs for gasphase acetonitrile, propionitrile and acrylonitri le in remarkable agreement with experiment (average absolute deviation 0.09 eV). The CEBEs of these systems confirm the overall trends of th e previous attributions of their respective gas-phase XPS spectrum, ex cept in the case of propionitrile. These results, as well as those on 2-cyanopropane, methacrylonitrile and 2-methylglutaronitrile, bring so me additional information on the extrapolation of the results to the a ssignment of the C 1s contributions of polyacrylonitrile. (C) 1997 Els evier Science B.V.