Coupled‐cluster study of the equilibrium geometry and harmonic vibrational frequencies of the methyl radical

Accurate equilibrium geometries, harmonic vibrational frequencies, and equilibrium rotational constants of the methyl radical were computed using coupled‐cluster theory in combination with the cc‐pV n Z and cc‐pCV n Z basis sets of Dunning. Valence and all electron calculations were carried out. Using all electron correlations and CBS extrapolation, the r e value is equal to 1.0758 Å, which is 0.0032 Å shorter than the experimental value of r 0 (1.079 Å). The harmonic (ω 1 , ω 2 , ω 3 , and ω 4 ) frequencies calculated using the CBS extrapolation differ from the experimental fundamental frequencies, respectively, by +142, +125, +21, and –82 cm −1 . © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005