Vibrational Spectrum and Thermochemistry of the Formyl (HCO) Radical:  A Variational Study by the Coupled Cluster CCSD(T) Method with Complete Basis Set Extrapolation

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-ζ 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 calculation 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 C_p°, S°, and (H_T° − H₀°) are presented for temperatures up to 2000 K.