Research Information System
INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, vol.120, no.16, 2020 (SCI-Expanded)
Multi-reference configuration interaction, MR-CI (including extensivity corrections, named +Q), calculations were performed on the S-0-S(3)states of cyclohexa-2,4-diene-1-thione (thione24) and cyclohexa-2,5-diene-1-thione (thione25), which are thione isomers of thiophenol. Several types of uncontracted MR-CIS and MR-CISD wavefunctions were employed, comprising MR-CI expansions as large as similar to 365 x 10(6)configuration state functions. The nature of the studied excited states was characterized. Vertical excitation energies (Delta E) and oscillator strengths (f) were computed. The most intense transitions (S-0 -> S(2)for24and S-0 -> S(3)for25) do not change with the wavefunction, although a variation as large as similar to 1 eV was obtained for the S(3)state of24, at the highest (MR-CI+Q) level. On the other hand, Delta Echanges at most by similar to 0.56 eV for25as the wavefunction changes, at the same level. The S(1)state of both thiones was found to have n pi* character and is in the visible region. For24, S(2)and S(3)are pi pi* and n pi* states, respectively, while for25the reverse order is obtained. S(2)and S(3)are in the range similar to 3.5 to 5.2 eV, again at the highest level. It is the first time that the excited states of the title molecules are studied. The computed results agree with the experimental onset of photoreactions of thiones24and25found by Reva et al (Phys. Chem. Chem. Phys.,2015,17, 4888).