Ion chemistry in XH4/Allene (X = Ge, Si) Gaseous Mixtures – Formation of X-C Bonds

The gas-phase ion chemistry of germane/allene and silane/allene mixtures has been studied, with the aim of obtaining information on the experimental conditions leading to the formation of clusters of increasing size containing Ge or Si bonded to carbon atoms. Mechanisms of ion/molecule reactions have been elucidated by ion-trap mass spectrometry using single and multiple isolation steps. Rate constants for the most important reactions have been determined experimentally and compared with collisional rate constants. The germane/allene mixtures display a low reactivity and the most abundant germanium and carbon containing ion is GeCHmath image. However, chain propagation proceeds after the first nucleation step, even if rather slowly, with the formation of large clusters such as Ge4C3Hmath image at low abundance. In contrast, the silane/allene mixtures are very reactive and many different processes are observed, with the formation of several silicon and carbon containing ions with appreciable efficiency. Chain propagation proceeds mainly through reactions of silicon-containing ions with allene molecules and the subsequent formation of large clusters such as Si3C3Hmath image and Si4C3Hmath image.