An electron impact investigation of pentafluoroethyl iodide

Abstract

An electron impact investigation on C 2F 5I was made using the Retarding Potential Difference technique in a Bendix time-of-flight mass spectrometer. Appearance potentials were measured as follows: CF 3 +, 13.73 eV; C 2F 5 +, 11.71 eV; and C 2F 5I +, 10.66 eV. From these results and previously published values it is possible to derive Δ H f 0(C 2F 5I) ⩾ −236.4 kcal mol −1; Δ H f 0(C 2F 5I +) ⩽ +9.4 kcal mol −1, and D(C 2F 5I) ⩽ 47.0 kcal mol −1. Observation of certain reaction channels in a parallel Ion Cyclotron Double Resonance experiment suggests that Δ H f 0(C 2F 4I +) = +82.0 ± 2 kcal mol −1. From the latter result it is also possible to derive that D(FC 2F 4I +) = 91.5 kcal mol −1. In principle, D(CF 3CF 2I) could also be established if Δ H f 0(CF 2I) were known. If D(FCF 2I) is estimated as 120 kcal mol −1, then Δ H f 0(CF 2I) = −40 kcal mol −1, and D(CF 3CF 2I) ⋍ 79 kcal mol −1. Uncertainties of ±0.1 eV are assigned to appearance potentials and ±2 kcal mol −1 to heats of formation.