Theoretical study on the electronic absorption spectra of C3Cl and its ions

Optimized geometries of small carbon clusters C3Cl and its ions in their ground and selected excited states have been obtained by CASSCF approach. The vertical excitation energies for the electronic excitations to low-lying excited states have been calculated by the CASPT2 method using cc-pVTZ basis set. The predicted vertical excitation energies are in good agreement with available experimental values. The spin-orbit effect on the spin-forbidden transitions is generally small, with oscillator strengths in the magnitude of 10−7-10−13. The vertical emission energies for the selected excited states were calculated at CASPT2/cc-pVTZ level of theory based on the CASSCF optimized geometries of the corresponding excited states.