The structure of gas phase tin oxide ions generated by laser ablation: A combined Fourier transform mass spectrometry and density functional theory study

The radical ion series (SnO)(2-6)(+), (SnO)(2-6)(-), (SnO)(0-5)Sn+ and (SnO)(1-6)O- have been generated by the high power laser ablation of SnO and SnO2 targets positioned inside an ICR cell. In all ablation spectra obtained, and for any particular size Sn-x core, the tin-rich clusters (SnO)(x)Sn+ were more abundant than the corresponding oxygen-equivalent clusters (SnO)(x)(+), while the oxygen-rich clusters (SnO)(x)O- were always more abundant than the oxygen-equivalent clusters (SnO)(x)(-). High yields of the ions (SnO)(1,3)Sn+, (SnO)(3,6)O- and (SnO)(-)(6) suggest high stabilities for these species. Low energy CID studies revealed that loss of neutral (SnO)(x) units is the preferred, and for most ions investigated the exclusive, dissociation pathway. Global minima for the smaller cations and anions are proposed on the basis of local density functional theory (DFT) calculations. Calculated dissociation energies for the neutral and charged clusters were found to compare well with effusion cell and FTICR results. DFT also predicts that, for any cluster with the same size Sn-x core, IE(SnO)(x)EA(SnO)(x). A correlation between ion abundances and DFT heats of formation is evident, and the ground state geometries provide insight into the evolution of structural versus size trends. Without assistance from the calculations, erroneous conclusions regarding the structures of the experimentally-sampled clusters might have been drawn from the low energy CID results.