107396-35-0Relevant academic research and scientific papers
Gas-Phase Reactions of Si+(2P) with Small Hydrocarbon Molecules: Formation of Silicon-Carbon Bonds
Wlodek,Fox,Bohme
, p. 4461 - 4468 (2007/10/02)
Reactions of ground-state Si+(2P) ions have been investigated with the hydrocarbon molecules CH4, C2H6, C2H4, C2H2, CH2CCH2, CH3CCH, and C4H2 proceeding in a helum bath gas at 0.35 Torr and a temperature of 296 ± 2 K with the selected-ion flow tube (SIFT) technique. A range in the nature and degree of reactivity was observed. Methane reacts slowly to form an adduct ion. Results of quantum chemical calculations performed at the UMP4(SDTQ)/6-31G**// UHF/6-31G** level are presented which provide insight into the possible structure of this adduct ion. Adduct formation also is a strong feature in the reactions of Si+ with C2H2 and C2H4 in which it competes with condensation resulting in H atom elimination. The reaction with C2H6 predominantly leads to Si-C bond formation in the product ions together with elimination of CH3, CH4, or H2. For these three reaction channels possible mechanisms are proposed involving C-C and C-H bond insertion. The reactions with allene and propyne are rapid and have similar product distributions. Several bimolecular product channels are observed and all lead to Si-C bond formation. The reaction with diacetylene is unique in that it proceeds rapidly only by hydride ion transfer. Higher order reactions leading to more complex silicon-carbide ions have also been characterized. The reactivities of the Si+ reactions are compared with those available for the analogous reactions with C+ proceeding under similar conditions of temperature and pressure. Except for the reactions with allene and propyne, the reactions with Si+ are uniformly slower and less efficient than the corresponding reactions with C+, and the competition with adduct formation is not apparent for the reactions with C+ in which charge transfer and H atom elimination are sometimes more predominant. The observation and failure to observe reactions at 296 K is used to provide insight into the standard enthalpies of formation of the silicon-containing hydrocarbon ions SiCH2+, SiCH3+, SiC2H+, SiC2H3+, SiC2H2+, SiC2H4+, SiC2H6+, SiC3H3+, SiC4H5+, and SiC4H+. A brief discussion is presented of the implications of the chemistry observed with Si+ for the formation of molecules containing Si-C bonds in partially ionized environments containing silicon and carbon, such as the circumstellar envelopes of carbon stars.
