Accurate density functional calculatiuon of core-electron binding energies: Part V : application to nitriles. Model molecules for polyacrylonitrile revisited

A recent procedure for computing accurate core electron binding energies (CEBEs) via density functional theory (DFT) is applied to acetonitrile, propionitrile, 2-cyanopropane, acrylonitrile, methacrylonitrile and the 2-methylglutaronitrile conformer of lowest energy. The first three systems have been studied in the past as model compounds to interpret the XPS spectrum of polyacrylonitrile (PAN) using post-Hartree–Fock finite-difference calculations, in order to solve a controversy in the assignment of chemically shifted atoms in the C 1s region. This assignment is revisited with the unrestricted generalized transition-state 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 predicted CEBEs for gas-phase acetonitrile, propionitrile and acrylonitrile in remarkable agreement with experiment (average absolute deviation 0.09 eV). The CEBEs of these systems confirm the overall trends of the previous attributions of their respective gas-phase XPS spectrum, except in the case of propionitrile. These results, as well as those on 2-cyanopropane, methacrylonitrile and 2-methylglutaronitrile, bring some additional information on the extrapolation of the results to the assignment of the C 1s contributions of polyacrylonitrile.