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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-z
quality. The complete basis set limits for the equilibrium geometry and
spectroscopic parameters of HCO were estimated: Re(CH) = 1.117
Angs; Re(CO) = 1.174 Angs; alphae(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 (298.15 K)
was found using the basis set of cc-pcv5z quality: 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. The potential energy surface for the ground state of HCO was
obtained with 133 single-point energies calculated with use of the augmented
correlation-consistent polarized basis sets of triple-, quadruple-, and
quintuple-z quality and extrapolated then to the complete basis set level.
Calculations are at the coupled-cluster singles and doubles level augmented
by a perturbative correction for connected triple excitations CCSD(T). The
relativistic and core-valence corrections were taken into consideration. A
variational calculations of the HCO vibrational spectrum was performed in a
basis of products of the eigenfunctions of harmonic oscillators expressed
through Hermite polynomials. Infrared intensities of the lowest excitations
were evaluated through calculations of matrix elements of the dipole moment
for the relevant transitions. The expectation values of the structural and
rotational parameters of HCO were computed. Values of Cp, S, and
(HT - H0) are presented for temperatures up to 2000 K. |
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