Mass Spectrometric Study of the Photoionization of Some Fluorocarbons and Trifluoromethyl Halides.

The photoionization curves and the threshold energies for the molecule and several abundant fragment ions of CF4 C2F6, C3F8, C4F10, CF3H, CF3Cl, CF3Br, and CF3I have been measured. The threshold energies are correlated and the ionic heats of formation and some bond dissociation energies are calculated. It is apparent that the values obtained for the CF 3 + ions are not the adiabatic ones, but include large amounts of excess energy. This excess is the lowest for the CF 3 + from CF3I for which an explanation is suggested. Assuming that the excess is not zero for the last compound we obtain the following upper limits: Δ H f 0 ° ( CF 3 ) + ⩽ + 365.3 kJ mol  - 1 = + 87.3 kcal mol - 1 ; I(CF3) + ⩽ 8.62 eV; I(C2F5) + ⩽ 8.72 eV; I(C3F7) + ⩽ 8.70 eV; I(C4F9) + ⩽ 8.68 eV. From the mean value D(C p - C p ) = 402 ±2 kJ mol-1 = 96.0 ± 0.5 kcal mol-1 the bond dissociation energies D(C p - C s ) = 363 ± 3 kJ mol-1 = 86.8 ± 0.8 kcal mol-1 and D(C s - C s ) = 337 ± 4 kJ mol-1 = 80.6 ± 1.0 kcal mol-1 and D(C p - F) = 525 kJ mol-1 = 125.7 kcal mol-1 are calculated.