Reactions of Fe Ions (3 ≤ n ≤ 12) with ethane, ethylene and acetylene – reaction paths and rate constants –

We report on measurements of absolute rate constants of the reaction Fe + M → Fe n (M–2H) + + H 2 , with M = ethane, ethylene, and acetylene. The clusters were prepared by sputtering and the reactions took place in the ICR cell of a FT mass spectrometer. With acetylene, all clusters with 4 ≤ n ≤ 13 react and the rate constants do not display any significant size dependence. With ethylene Fe and Fe react, but the latter with a markedly smaller rate. Only Fe shows a detectable rate with ethane. Fe 4 H + does not, however, react with ethane. The addition of H to iron cluster ions can also have the opposite effect; with acetylene Fe 3 H + reacts, while Fe does not. – It appears that pronounced size specificities are more likely the more saturated the reacting molecule is. This statement is corroborated by results of earlier work with other molecules.