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Coupled Cluster CCSD(T) Calculations of Equilibrium Geometries, Anharmonic Force Fields, and Thermodynamic Properties of the Formyl (HCO) and Isoformyl (COH) Radical Species

Aleksandr V. Marenich and James E. Boggs*

Institute for Theoretical Chemistry, Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712

J. Phys. Chem. A, 2003, 107 (13), pp 2343–2350

DOI: 10.1021/jp0223298

Publication Date (Web): March 8, 2003

To whom correspondence should be addressed. Fax: (512) 471-8696. E-mail: james.boggs@mail.utexas.edu.

Abstract

The HCO and COH formyl radical species were studied by the coupled cluster electron correlation technique and using the augmented correlation consistent polarized core-valence basis sets of quadruple-ζ quality. The complete basis set limits for the equilibrium geometry and spectroscopic parameters of HCO were estimated: R_e(CH) = 1.117 Å; R_e(CO) = 1.174 Å; α_e(HCO) = 124.6°. The COH isomerization energy is equal to 176 kJ/mol. The energy of the COH → HCO transition state is equal to 107 kJ/mol. The heat of formation was found using the basis set of cc-pcv5z quality: Δ_fH°(298.15) = 42.3 for HCO and 218.1 kJ/mol for COH. The thermochemistry of HCO and COH was studied beyond the rigid rotor harmonic oscillator approach. The results were compared with available experimental data and results of previous calculations.

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