The spectroscopy of thioformaldehyde. MR-CI studies on the triplet states of H2CS Original Research Article

Using multireference CI methods, the CS stretching (C2v) and out-of-plane (Cs) potentials were calculated for triplet states of H2CS. From the CS stretch potentials the adiabatic excitation energies, CS equilibrium distances, vibrational frequencies and Franck-Condon (FC) factors were evaluated. Both the 3(σ, π∗) and 3(π, π∗) ← X̃ systems are predicted to be FC active, leading to long progressions. The 3(σ, π∗) state is found in the same energy region as S2, and may therefore play a role in the unusual photo-chemistry and photo-physics assocaited with S2 ← S0. It is shown that 3(π, π∗) is nonplanar, with a stabilization of ∼ 0.05 eV over the planar configuration, having RCS = 3.48 a0 and an out-of-plane angle of ∼ 28°. Also, 3(σ, π∗) is predicted to be nonplanar, with RCS = 3.55 a0, θ ∼ 56° and a stabilization energy of ∼ 0.17 eV. The 3(π, π∗) ← X̃ system, while predicted to be weak, lies in an energy region free from other states. Electron impact spectroscopy offers the best chance of observing this system. Vertical excitation energies and dipole moments will also be given.