Insight into ethylene interactions with molybdenum suboxide cluster anions from photoelectron spectra of chemifragments

Recent studies on reactions between MoO cluster anions and HO/CH mixtures revealed a complex web of addition, hydrogen evolution, and chemifragmentation reactions, with chemifragments unambiguously connected to cluster reactions with CH. To gain insight into the molecular-scale interactions along the chemifragmentation pathways, the anion photoelectron (PE) spectra of MoCH, MoCH, MoOCH, and MoOCH formed directly in MoO + CH (x > 1; y ≥ x) reactions, along with supporting CCSD(T) and density functional theory calculations, are presented and analyzed. The complexes have spectra that are all consistent with η-acetylene complexes, though for all but MoCH, the possibility that vinylidene complexes are also present cannot be definitively ruled out. Structures that are consistent with the PE spectrum of MoCH differ from the lowest energy structure, suggesting that the fragment formation is under kinetic control. The PE spectrum of MoOCH additionally exhibits evidence that photodissociation to MoO + CH may be occurring. The results suggest that oxidative dehydrogenation of ethylene is initiated by Lewis acid/base interactions between the Mo centers in larger clusters and the π orbitals in ethylene.