Abstract
The complete active space self-consistent field and multiconfigurational second-order perturbation theory methods have been used to investigate the low-lying electronic states of the HCCO radical and its anion. The calculated geometrical structure and harmonic vibrational frequencies for the X 2A″ state of HCCO are in good agreement with experimental values. The barrier to 12П (12A′) is estimated to be 0.069 eV (554 cm−1), which is also close to experimental result (540 cm−1). Moreover, we find that the 22A′ state is bent, while 22П (22A″) is linear. By comparing the oscillator strengths and adiabatic excitation energies, we show that the 22П (22A″) ← X 2A″ transition is the most intense among these transitions. The unpaired electrons mainly locate on the C atoms in the 22A′ and 22П (22A″) states according to the Mulliken spin populations. On the other hand, for HCCO−, the first adiabatic and vertical detachment energies are 2.210 and 2.362 eV, respectively, which reasonably agree with experimental value of 2.338 ± 0.008 eV. Remarkably, we explore several higher excited states of the HCCO radical (14A′, 24A″ and cis-14A′) and its anion (13A″, 11A″ and 13A′), which have not been reported in previous studies.
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