Gaseous ion reactions in SiF4 and SiF4–D2 mixtures

The gas-phase reactions of D+2, D+3, SiF+, and SiF+3 with SiF4 and of SiF+ and SiF+3 with D2 have been studied in the center-of-mass energy range of 0.2–7 eV using a tandem mass spectrometer. Only one reaction of a silicon-containing ion with SiF4 was observed, namely the highly endothermic transfer of F− from SiF4 to SiF+. Hence the SiF4 molecule must be almost unique in showing a virtual absence of gas-phase ionic chemistry in pure SiF4 subjected to ionization. Several ion-molecule reactions were observed in the SiF4–D2 system but of these only the dissociative F− transfer from SiF4 to D2+ is exothermic. The almost total absence of exothermic ion-molecule reactions means that the ionic distribution pertinent to the plasma chemistry of the SiF4 and SiF4–H2 systems will be determined solely by the cross sections of the electron impact ionization processes.