Growth of fluorocarbon macromolecules in the gas phase: IV. Li ⁺-attachment mass spectrometric investigation of high-mass neutral radicals in the downstream region of Ar/c-C₄F₈ plasmas

Mass analysis has been conducted on neutral species in the downstream region of Ar/c-C₄F₈ plasmas by Li⁺-attachment mass spectrometry. Various peaks appeared in the mass spectrum observed in the case of 29% c-C₄F₈, and many of them have unambiguously been assigned to the Li⁺ adducts of neutral radicals with odd-numbered fluorine atoms from 2n + 1 to 2n - 5, where n means the number of carbon atoms, as well as neutral species with even-numbered fluorine atoms from 2n + 2 to 2n - 10. In contrast, only the peaks due to C_nF _2n+2 (n = 1-7), C_nF_2n (n = 1, 4-8), C _nF_2n-2 (n = 3, 5-8) and C₉F₁₄ appeared in the case of 2.2% c-C₄F₈. These findings demonstrate that the Li⁺-attachment ionization is fragment-free, not only for relatively stable perfluorocarbon species but also for their neutral radicals, and therefore effective for the identification of high-mass neutral perfluorocarbon radicals. The analysis of the growth mechanisms of C _nF_2n+2 and C_nF_2n on the basis of thermochemistry has proposed CF₃CF as an important reactant.