Experimental and theoretical study of the formation of germanium-carbon ion species in gaseous germane/ethene mixtures.

The gas-phase chemistry of gaseous germane/ethene mixtures has been investigated by ab initio theoretical calculations and by experiments to examine the formation and growth of germanium-/carbon-containing species. Ion/molecule reactions in GeH4/C2H4 mixtures have been studied with an ion trap mass spectrometer. Ion abundance variations as a function of reaction time, reaction paths originating from primary ions of both reagents, and reaction rate constants of the main processes have been determined. The highest yield of new Ge-C bonds formed via reactions of Ge-containing ions with ethene molecules was obtained in mixtures carrying similar amounts of germane and ethene. Reactions of GeH2.+ with ethene play a prominent role in this system. High-level theoretical methods were therefore used to determine the geometrical structures and energies of transition structures, reaction intermediates, and final products for several reaction pathways. Formation of the adduct between GeH2.+ and H2C=CH2 is the initial step. This process is fairly exothermic, and the free energy of the system allows several transformations. Isomerization pathways and H, H-2, or CH3. loss pathways starting from this adduct have been explored. The free energy threshold defined by the first step shows that some transformations are likely to occur, whereas others can be regarded as inaccessible. Last, two theoretical methods have been used to compute the heats of formation of the attainable GeC2Hn+ species.