Structure of the\nSe<sub>4</sub> IsomersAn\nAb Initio Study

This study investigates the equilibrium geometries of\nfour different\nSe<sub>4</sub> isomers using the coupled cluster single and double\nperturbative (CCSD(T)) method, extrapolating to the complete basis\nsets. The ground-state geometry of the Se<sub>4</sub> isomer with\nthe C<sub>2v</sub> structure (2.8715 Å, 2.1750 Å, and 88.4°)\nis found to be very close to other theoretical values (2.910 Å,\n2.224 Å, and 90.0°) for the SeSe and Se–Se\nbond lengths and valence angle. Additionally, the adiabatic electron\naffinity, vertical electron affinity, and vertical ionization energy\nare calculated. The multireference configuration interaction method\nwas used to calculate transitions from the singlet ground state to\nsome excited counterparts, including the vertical excitation energy,\noscillator strength, and main electronic configuration. The predicted\nwavelengths of electronic transitions to 1<sup>1</sup>B<sub>u</sub>, 1<sup>1</sup>A<sub>u</sub> with C<sub>2h</sub> symmetry, and 1<sup>1</sup>B<sub>1</sub> state with the C<sub>2V</sub> symmetry could\nmatch the experimental NIR absorption band at 710–850 nm. These\ntransitions and electronic properties may provide insights into the\nrole of selenium in astrophysical environments, where <sup>74</sup>Se in the solar system has been confirmed to originate from the supernova\nexplosion process. The theoretical results offer a deeper understanding\nof Se<sub>4</sub> electronic and geometric structures while also providing\ncrucial spectroscopic data that could aid in the identification of\nselenium-containing molecules in extraterrestrial environments.