ION-MOLECULE REACTIONS OF GROUP IVA ELEMENT

Several gas-phase ion-molecule reactions have been investigated using a tandem mass spectrometer. All of these reactions involved a molecule that incorporated a Group IVA element (carbon, silicon or germanium) in the reactant pair. In the first experiment conducted, the existence of GeH(,5)('+) was proven, and the proton affinity of germane was determined.;Studies of the major gaseous ion reactions occurring in SiF(,4) and SiF(,4)-D(,2) mixtures were also performed. Only one reaction of a silicon-containing ion with SiF(,4) was observed; namely, the highly endothermic transfer of F('-) from SiF(,4) to SiF('+). Several ion-molecule reactions were observed in the SiF(,4)-D(,2)('+) system, but of these only the dissociative F('- )transfer from SiF(,4) to D(,2)('+) is exothermic.;The search for a long-lived C(,3)H(,7)('+) collision complex was continued in the study of vinyl ions with methane. No persistent collision complex was ever directly detected, even at methane pressures up to 10('-2) torr. However, the excellent agreement of the isotopic distributions of allyl ion, propargyl ion, vinyl ion (from the back reaction) and the fraction of methyl ion in the C(,2)D(,3)('+)/CH(,4) and C(,2)H(,3)('+)/CD(,4) systems strongly suggests that a significant part of the reaction proceeds via a long-lived C(,3)H(,7)('+) complex. This indicates that the lifetime of the adduct is less than the transit time of the apparatus (20 microseconds), under all experimental conditions. A very significant part of the reaction that produces CH(,5)('+), CH(,3)('+) and C(,3)H(,6)('+) occurs via direct processes. Also, isotope labelling studies have shown that the only H-atoms that can be lost from the complex as atomic hydrogen, are those that originated from the C(,2)H(,3)('+) reactant. Hydrogens originating from the methane molecule are never lost as atomic hydrogen. A mechanism that is consistent with all of these facts is presented.;RRKM theory was used to help establish a potential energy profile for the reaction of vinyl ions with methane. Percentages for the fraction of back reacted products were calculated as a function of the energy barriers involved, and these were adjusted to give good agreement with the experimental values.