The ClO4 radical: a theoretical study on ground and excited states

In agreement with previous studies, the ground state of ClO4 has been confirmed to be X2B1. Vertical excitation energies and oscillator strengths were calculated by MRCI methods for doublet and quartet states of ClO4. The highest oscillator strength was found for 12A1 at 2.95 eV. This state has been identified as the upper state seen by Kopitzky and co-workers in the absorption spectrum of ClO4. Two higher states, 22A1 and 32A1, at 4.19 and 8.12 eV, respectively, also have relatively high oscillator strengths. Rydberg states start at about 9.5 eV. Geometry optimizations were performed by DFT and CCSD(T) methods. After extensive testing, the B3LYP density functional, together with the 6-311 + G(3df) basis set were chosen for calculations. Optimized geometries of seven excited states were obtained. The adiabatic excitation energy of 12A1 (2.40 eV) agrees closely with the observed band origin at 2.46 eV. Three excited states have one or two imaginary vibrational modes. Electron affinity and heat of formation of ClO4 agree with literature values. None of the quartet states was found to be stable.

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