Structures, Electron Affinities, and Harmonic Vibrational Frequencies of C₆H₅X/C₆H₅X^- (X = N, S, NH, PH, CH₂, and SiH₂)

The molecular structures and electron affinities of the C₆H₅X/C₆H₅X^- (X = N, S, NH, PH, CH₂, and SiH₂) species have been determined using seven different density functional or hybrid Hartree−Fock density functional methods. The basis set used in this work is of double-ζ plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. These methods have been carefully calibrated (Chem. Rev. 2002, 102, 231). The geometries are fully optimized with each density functional theory (DFT) method, and discussed. Harmonic vibrational frequencies were found to be within 3.2% of available experimental values for most functionals. Three different types of the neutral−anion energy separations reported in this work are the adiabatic electron affinity (EA_ad), the vertical electron affinity (EA_vert), and the vertical detachment energy (VDE). The most reliable adiabatic electron affinities, obtained at the DZP++ BPW91 level of theory, are 1.45 (C₆H₅N), 2.29 (C₆H₅S), 1.57 (C₆H₅NH), 1.51 (C₆H₅PH), 0.91 (C₆H₅CH₂), and 1.48 eV (C₆H₅SiH₂), respectively. Compared with the experimental values, the average absolute error of the BPW91 method is 0.04 eV. The B3LYP and B3PW91 functionals also gave excellent predictions, with average absolute errors of 0.06 and 0.07 eV, respectively.