Theoretical study of the molecular conformations, vibrational frequencies and thermochemistry of the FC(O)OOO(O)CF, FS(O_2)OOO(O_2)SF and FC(O)OOO(O_2)SF trioxides

摘要

The molecular structures, conformational mobilities, harmonic vibrational frequencies and thermochemistry of the FC(O)OOO(O)CF, FS(O_2)OOO(O_2)SF and FC(O)OOO(O_2)SF trioxides were studied by ab initio and density functional methods. The potential energy curves for the internal rotations were calculated using the B3LYP hybrid functional with the 6-311+G(3df) basis set. The equilibrium conformations are characterized by skew structure with dihedral angles COOO and SOOO of about 90° and 95°, respectively. The most stable structures were also calculated using the G3(MP2)B3 and G4(MP2) ab initio methods and with the functional M06-2X/6-311+G(3df). Average standard enthalpies of formation at 298K derived for FC(O)OOO(O)CF, FS(O_2)OOO(O_2)SF and FC(O)OOO(O_2)SF from isodesmic reactions energies calculated at the G3(MP2)//B3LYP/6-311++G(3df,3pd) and G4(MP2) levels of theory are predicted to be -195.4, -255.6, and -226.5kcalmol~(-1). From these values, OO bond dissociation enthalpies of 25-33kcalmol~(-1) were estimated.