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

Abstract

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 CnF2n+2 (n = 1–7), CnF2n (n = 1, 4–8), CnF2n−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 CnF2n+2 and CnF2n on the basis of thermochemistry has proposed CF3CF as an important reactant.