Intracluster Ion−Molecule Reactions of Ti+with Methanol Clusters

Abstract

The intracluster ion−molecule reactions occurring within the titanium/methanol heterocluster ions are studied using a simple cluster source based on the mixing of the laser-ablated plasma with the supersonic expansion of a methanol vapor seeded in Ar carrier gas. The product ions are detected using a reflectron time-of-flight mass spectrometer. The mass spectra exhibit a major sequence of cluster ions with the formula Ti+(CH3O)2(CH3OH)n, which are attributed to the hydrogen elimination reactions (−2H or −H2) of Ti+ ion within the heteroclusters. In addition, heterocluster ions of the types Ti+(CH3O)(CH3OH)n and Ti+(CH3O)3(CH3OH)n also emerge throughout the observed mass spectra, indicating that consecutive H-eliminations by the Ti+ ion occur for up to three methanol molecules. The results from isotope-labeling experiments suggest that H-elimination is the reaction path for O−H bond breaking in Ti+−methanol heteroclusters. The observed TiOH+ and TiO+ ions are interpreted as arising from the insertion of Ti+ ions into the C−O bond in CH3OH, followed by CH3- and CH4-elimination, respectively, from the [HO−Ti+−CH3] intermediate. The experiments also show that the chemical reactivity of heterocluster ions is greatly influenced by cluster size and argon stagnation pressure. The reaction energetics and formation mechanisms of the observed heterocluster ions are also discussed.