Bis(trifluoroaceto) disulfide (CF3C(O)OSSOC(O)CF3): a HeI photoelectron spectroscopy and theoretical study

Bis(trifluoroaceto) disulfide CF(3)C(O)OSSOC(O)CF(3) was prepared and studied by Raman, photoelectron spectroscopy (PES), and theoretical calculations. This molecule exhibits gauche conformation with both C=O groups cis to the S-S bond; the structure of the OSSO moiety is characterized by dihedral angle delta(OSSO) = -95.1 degrees due to the sulfur-sulfur lone pair interactions. The contracted S-S bond (1.979 Angstroms) and relatively high rotational barrier (19.29 kcal mol(-1) at the B3LYP/6-31G level) of the delta(OSSO) indicate the partial resonance-induced double bond character in this molecule. After ionization, the ground cationic-radical form of CF(3)C(O)OSSOC(O)CF(3)(*+) adopts a trans planar main-atom structure (delta(OSSO) = 180 degrees and delta(OCOS) = 0 degrees ) with C(2)(h) symmetry. The S-S bond elongates to 2.054 Angstroms, while the S-O bond shortens from 1.755 Angstroms in neutral form to 1.684 Angstroms 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: 3ppi {36a (n(A)(S))](-1) and 3ppi [35b (n(B)(S), n(B)(O(C)(=)(O)))](-1), with an experimental energy separation of 0.16 eV. The first vertical ionization energy is determined to be 10.81 eV.