The molecular structure, spin–vibronic energy levels, and thermochemistry of CH3O

Ab initio calculations of the molecular structure and thermochemical properties of the methoxy CH3O radical were performed. Partition functions were calculated beyond the ‘standard’ rigid rotor-harmonic oscillator approach by means of the explicit summation of eigenenergies of a spin–vibronic Hamiltonian that included the linear, quadratic, cubic, and quartic Jahn–Teller terms with account for all important anharmonic effects. The heat of formation ΔfH298.15K∘(CH3O)=23.3±0.9 kJ/mol was evaluated by a study of the reactions of C–H and C–O bond dissociations and atomization of CH3O. Total energies computed with the use of the coupled cluster electron correlation technique CCSD(T) were extrapolated to the complete basis set limit with account for spin–orbit, scalar relativistic, and core–valence correlation corrections.