Gas-phase reactivity of hexanuclear molybdenum [Mo6I14]2− and its photo-fragments towards O2 and CO2: combined mass spectrometry (MSn) and quantum chemical simulations

Abstract

The optical properties, photo-decomposition and photo-reactivity of [Mo₆I₁₄]²⁻ clusters and their associated photo-products are examined in the gas phase. The UV-visible optical spectrum of the electron-rich [Mo₆I₁₄]²⁻ cluster is measured and the wavelength dependence of the principal fragments is interpreted on the basis of the quantum chemistry (QC) simulated spectrum and detailed transitions. A special focus of attention is the photo-generated [Mo₆I₁₄]⁻ and photo-specific radical [Mo₆I₁₃]²⁻˙ as well as halogen-depleted clusters [Mo₆I_n]⁻ with n < 14. The fragmentation and reaction energetics of all species are examined with a combination of mass spectrometry experiments, ion–molecule reactions with O₂ and CO₂ under irradiation and QC simulations. Reactions with O₂ are shown to be very exergonic with up to 5 eV release when O₂ is dissociated on the cluster. Experimental evidence for the photo-decomposition of CO₂ into CO and O on [Mo₆I_n]⁻ ions is provided together with detailed QC energetics.