Theoretical study of electronic spectra of linear carbon clusters HC2nS (n = 1–5)

In this work we report the structures and stabilities of linear carbon clusters HC_2nS (n = 1–5) in their ground states using the B3LYP density functional. The rotational constants at the optimized geometries give excellent agreement with the experimental and previous theoretical values. The vertical excitation energies of the 2²Π ← X²Π transitions at the CASPT2 level are 3.16, 2.66, 2.05, 1.78, and 1.55 eV, respectively, in good agreement with the corresponding observed values of 3.01, 2.48, 2.10, 1.84, and 1.65 eV. Also, the exponential-decay curves for these vertical excitation energies obtained from experiments and theoretical calculations are illuminated.