Electron attachment to the perfluoroalkanes n-C/sub N/F/sub 2N/+2 (N = 1--6) and i-C4F10

Parent and fragment negative ion formation from seven perfluoroalkanes [n-C/sub N/F/sub 2N/+2 (N = 1--6) and i-C4F10] under low-energy (0--10 eV) electron impact has been studied using a time-of-flight mass spectrometer. For CF4, C2E6, and C3F8 only fragment anions were observed, F- being the most abundant. For n-C4F10 a weak parent ion was observed, but again the predominant ion was F-. For i-C4F10, n-C5F12, and n-C6F14 the parent negative ions were the most abundant with relative cross sections peaking at 0.6 eV and autodetachment lifetimes from 10 to 100 μs depending on the molecular size and electron energy. In addition to the parent negative ion and the F- ion, fragment negative ions of the form C/sub N/F-/sub 2N/+1, C/sub N/F-/sub 2N/, C/sub N/F-/sub 2N/-1 (with N = 1--6) have been detected. The relative cross sections for all observed negative ions have been measured and corrected for the finite width of the electron pulse using an unfolding procedure. The positions of the dissociating negative ion states (NISs) shift to lower energies with increasing size of the molecule. Possible fragmentation mechanisms of the NISs leading to the production of the observed fragment negative ions have been suggested and discussed. From the appearance onsets of a number of fragment negative ions, various C--C and C--F bond dissociation energies, heats of formation, and electron affinities EA of certain fragments have been determined and are reported