Hydrogenation reactions of neutral carbon clusters: C n ( n=6–75)+D 2

Abstract

The hydrogenation reactions of neutral carbon clusters, C n +D 2 , are examined over a wide range of cluster sizes, n =6–75. Clusters are created by pulsed laser vaporization of graphite and react with D 2 in a pulsed, fast-flow reactor. After supersonic expansion and collimation the cluster reactants and products are photoionized at 118.2 nm and mass analyzed via high-resolution time-of-flight mass spectrometry. The observed ion signals provide information both on the decay of the C n reactants and on the formation of the C n D m products. From the product appearance kinetics, we conclude that C n D m are formed via sequential D-atom addition and that, in some cases, loss of carbon may accompany hydrogenation. The C 2 n for n ≤20 show a preference for formation of C n D 2 , consistent with production of long-chain polyacetylenes. From fits to the decay of C n signals, we determine the relative rate for the overall reaction as a function of cluster size. The observed drop in reactivity for C 2 n near n =18 correlates well with the onset of the closed-shell fullerenes.