FORMATION, SPECTROSCOPY, PHOTOCHEMISTRY, AND QUANTUM-CHEMISTRY OF THE(S-2)(O-2) COMPLEX IN SOLID ARGON

Samples formed by codepositing S-2 from a superheater source with Ar/O -2 on a 10 K substrate exhibit very strong 1403.0-cm(-1), and weaker 7 25.5-cm(-1) infrared absorptions. Photolysis decreases these bands sli ghtly and produces SO2 and S2O. The infrared bands show O-18(2) and S- 34(2) Shifts appropriate for O-O and S-S fundamental vibrations, and t riplet absorptions in mixed isotopic experiments suggesting two equiva lent O and two equivalent S atoms in the product complex. Similar resu lts were obtained for Se-2 and O-2; new absorptions appeared at 1404.5 and 391 cm(-1). Ab initio calculations at the SCF, CISD, and CCSD lev els of theory failed to find a complex with the observed spectroscopic properties. However, calculations with the BP density functional char acterized a singlet (S-2)(O-2) parallelogram structure bound by 15.6 k J/mol relative to triplet S-2 and O-2 With the O-O stretching frequenc y red-shifted 187 cm(-1) and the S-S fundamental blue-shifted 20 cm(-1 ). This weakly bound (S-2)(O-2) complex is chemically intermediate bet ween the unstable O-4 and stable S-4 molecules. The argon matrix has m ade possible the formation of the weak (S-2)(O-2) complex and DFT with the BP functional has characterized this weak charge-transfer interac tion.