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Abstract

The gas-phase infrared spectrum of Ti₄O₁₀^- is studied in the spectral range from 400 cm^–1 to 1250 cm^–1 using cryogenic ion trap vibrational spectroscopy, in combination with density functional theory (DFT). The infrared photodissociation (IRPD) spectrum of D₂-tagged Ti₄O₁₀^- provides evidence for a structure of lower symmetry that contains a superoxo group (1121 cm^–1) and two terminal Ti=O moieties. DFT combined with a genetic algorithm for global structure optimization predicts two isomers which feature a superoxo group: the C_s symmetric global minimum-energy structure and a similar isomer (C₁) that is slightly higher in energy. Coupled cluster calculations confirm the relative stability. Comparison of the harmonic DFT spectra (different functionals) with the IRPD spectrum suggests that both of these isomers contribute. Earlier assignments to the adamantane-like C_3^v isomer with three terminal Ti–O^• – groups in a quartet state are not confirmed. They were based on the infrared multiple photon photodissociation (IRMPD) spectrum of bare Ti₄O₁₀^- and local DFT structure optimizations.