Intramolecular ion-molecule reactions within Ti⁺(CH ₃COCH₃)_n heteroclusters: Oxidation pathway via C=O bond activation

A laser ablation-molecular beam/reflectron time-of-flight mass spectrometric technique was used to investigate the ion-molecule reactions that proceed within Ti⁺(CH₃COCH₃)_n heterocluster ions. The reactions of Ti⁺ with CH₃COCH ₃ clusters were found to be dominated exclusively by an oxidation reaction, which produced TiO⁺(CH₃COCH₃) _n clusters. These ions were attributed to the insertion of a Ti ⁺ ion into the C=O bond of the acetone molecule within the heteroclusters, followed by C₃H₆ elimination. The mass spectra also indicated the formation of minor sequences of heterocluster ions with the formulas Ti⁺(C₃H₄O)(CH ₃COCH₃)_n and TiO⁺(OH)(CH ₃COCH₃)_n, which could be attributed to C-H bond insertion followed by H₂ elimination and to the sequential OH abstraction by the TiO⁺ ion, respectively. Density functional theory calculations were carried out to model the structures and binding energies of both the association complexes and the relevant reaction products. The reaction pathways and energetics of the TiO⁺ + CH₂CHCH₃ product channel are presented.