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

Abstract

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 C 3 , C 5 , C 6 , and C 9 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 C 1 to C 10 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 C 7 cluster. On the basis of the predicted concentration invariance with temperature for C 7 , 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 C 7 .