Bis(trifluoroaceto) Disulfide (CF3C(O)OSSOC(O)CF3):  A HeI Photoelectron Spectroscopy and Theoretical Study.

Bis(trifluoroaceto) disulfide CF3C(O)OSSOC(O)CF3was prepared and studied by Raman, photoelectron spectroscopy (PES), and theoretical calculations. This molecule exhibits gauche conformation with both CO groups cis to the S−S bond; the structure of the OSSO moiety is characterized by dihedral angle OSSO−95.1° due to the sulfur−sulfur lone pair interactions. The contracted S−S bond (1.979 Å) and relatively high rotational barrier (19.29 kcal mol-1at the B3LYP/6-31G level) of the OSSOindicate the partial resonance-induced double bond character in this molecule. After ionization, the ground cationic-radical form of CF3C(O)OSSOC(O)CF3•adopts a trans planar main-atom structure (OSSO180° and OCOS0°) with C2hsymmetry. The S−S bond elongates to 2.054 Å, while the S−O bond shortens from 1.755 Å in neutral form to 1.684 Å in its corresponding cationic-radical form. The adiabatic ionization energy of 9.91 eV was obtained accordingly. The first two HOMOs correspond to the electrons mainly localized on the sulfur 3p lone pair MOs:  3p 36a (nAS)-1and 3p 35b (nBS, nBO(CO))-1, with an experimental energy separation of 0.16 eV. The first vertical ionization energy is determined to be 10.81 eV. [ABSTRACT FROM AUTHOR]