Structures, Electron Affinities, and Harmonic Vibrational Frequencies of the Simplest Alkyl Peroxyl Radicals and Their Anions

The molecular structures and electron affinities of the R-OO/R-OO⁻ (R = CH₃, C₂H₅, n-C₃H₇, n-C₄H₉, n-C₅H₁₁, i-C₃H₇, t-C₄H₉) 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-type and p-type functions, denoted DZP++. The geometries are fully optimized with each density functional theory method. Harmonic vibrational frequencies were found to be within 3.1% of available experimental values for most functionals. Two different types of the neutral−anion energy separations reported in this work are the adiabatic electron affinity and the vertical detachment energy. The most reliable adiabatic electron affinities obtained at the DZP++ BP86 level of theory are 1.150 (CH₃OO), 1.124 (C₂H₅OO), 1.146 (n-C₃H₇OO), 1.173 (n-C₄H₉OO), 1.184 (n-C₅H₁₁OO), 1.145 (i-C₃H₇OO), and 1.114 eV (t-C₄H₉OO). Compared with the experimental values, the average absolute error of the BPW91 method is 0.05 eV.