A theoretical study on the equilibrium structures, vibrational frequencies and photoelectron spectroscopy of thiocarbonyl fluoride by using density functional and coupled-cluster theories

- The properties of F2CS were computed by DFT and CC approaches.
- The photoelectron spectra were simulated by computing Franck-Condon factors.
- Computed equilibrium geometries are reliable assessed from the following criteria.
- The simulated spectra are in agreement with the experiment.
- The computed adiabatic ionization energies are of high accuracy.

The equilibrium geometries, vibrational frequencies and normal modes of F2CS and F2CS+X∼2B2, A∼2B1, and B∼2A1 states were obtained by utilizing both density functional and coupled-cluster (CC2) theories. Franck-Condon factors were calculated by using the harmonic-oscillator model taking into account the Duschinsky effect, based on which photoelectron spectra were simulated. The adiabatic ionization energies were computed by the CCSD(T) method extrapolated to the complete basis set limit. The computed equilibrium structures and vibrational frequencies are generally in agreement with the experiment, except in few cases. The B3LYP and CC2 approaches perform equally well in the computations of F2CS. The simulated photoelectron spectra of F2CS are also in accord with the experiment, indicating that the calculated structures are reliable. The computed adiabatic ionization energies are in agreement with the experiment within 0.01, 0.02, and 0.06 eV for the three ionic states, respectively.