The Kinetics and Formation of Small Carbon Clusters in an Argon Matrix

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Abstract
Pure carbon clusters, formed by Nd/YAG laser ablation of graphite, have been trapped in an argon matrix at 12 K. The temperature dependence of the prominent infrared absorption bands attributable to C3 , C5 , C6 , and C9 clusters has been investigated between 12 K and 38 K. The former two are observed to decay and the latter two to grow with increased matrix annealing. A new kinetic model based on solid state diffusion theory and involving thermally activated diffusion and aggregation is introduced. All possible pairwise interactions of the linear carbon clusters from C1 to C10 are included in the model. The coupled differential equations are solved numerically and provide a reasonable fit to the experimental temperature profiles of the known clusters. Predictions emerge from the fit for the unknown matrix infrared frequencies for the C7 cluster. On the basis of the predicted concentration invariance with temperature for C7 , the infrared bands at 2128 cm-1 and 1894 cm-1 are ascribed to this linear cluster. This attribution supports the recent assignment of the gaseous 2138 cm-1 band to linear C7 .

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