Intracluster ion–molecule reactions of Ti + with ether clusters

Abstract

The intracluster ion–molecule reactions of Ti +(CH 3OR) n (R = CH 3, n-C 3H 7, n-C 4H 9, t-C 4H 9) complexes produced by the mixing of laser-vaporized plasmas and pulsed supersonic beams were investigated using a reflectron time-of-flight mass spectrometer (RTOFMS). The reactions of Ti + with dimethyl ether clusters were found to be dominated by the CH 3 elimination reaction, which produces Ti +(OCH 3) m (CH 3OCH 3) n clusters ( m = 1–3). The mass spectra resulting from the reactions of Ti + with the other ether clusters indicate the formation of major sequences of heterocluster ions with the formula Ti +(OCH 3) x (OR) y (CH 3OR) n , where x = 1–3 and y = 0–2. These sequences are attributed to the insertion of Ti + ions into the C O bonds of the ether molecules within the heteroclusters, followed by alkyl radical elimination. The prevalence of radical elimination of longer alkyl groups rather than of CH 3 radicals suggests that R elimination from the [CH 3O Ti + R] intermediate is the preferred decomposition pathway after the selective insertion of a Ti + ion into the C O bond of an OR group. Our results also indicate that consecutive insertions of a Ti + ion can occur for up to three precursor molecules. The experiments also show that the molecular eliminations of H 2 and alkanes, resulting from C H and C C bond insertion, respectively, play an increasingly important role as the size of the alkyl group (R) in the ether molecule increases. The reaction energetics and the formation mechanisms of the observed heterocluster ions are also discussed.