Corroding the chromium cation

Two [Cr,O₂]⁺ isomers have been selectively produced and studied by FT-ICR mass spectrometry. The Cr(O₂)⁺ complex was formed by supersonically expanding a plasma produced by laser vaporization of chromium metal with the helium carrier gas, which was seeded with traces of oxygen, while the chromyl cation is formed in an expansion with N₂O. The complex is stable against thermal collisions, but in a bimolecular reaction with water it is rapidly converted to the chromyl cation, with ligand exchange being only a minor side reaction. Isotopic studies suggest a side-on geometry for Cr(O₂)⁺, in accordance with density functional (B3LYP) calculations. The present work indicates that an investigation of the selected isomers can indeed be carried out, if appropriate chemical methods for the ion generation are applied.     

Infrared spectra and isomeric structures of hydroxide ion-water clusters OH- (H2O)1-5: a comparison with H3O (H2O)1-5

Size-selected hydroxide ion water tetramers and pentamers [OH-(H₂O)_4,5], produced by a supersonic expansion, have been investigated using vibrational predissociation spectroscopy in conjunction with ab initio calculations based on density functional theory (DFT). The observed spectra in the frequency range 2650–3850 cm^?1 show some broad absorption bands attributed to the free and hydrogen bonded OH stretches of OH-(H₂O)_4,5 at an estimated cluster temperature of 170 K. DFT calculations performed at the B3LYP/6-31 + G* level reveal five and eight possible low lying isomeric forms for OH-(H₂O)₄ and OH-(H₂O)₅, respectively. The global minimum isomer of the tetramer is tri-solvated cyclic, which is energetically more stable than the tetra-solvated wheel-shaped form with an OH- ion at its centre. Compact cage-like lowest energy structures are found for the pentamer, in which the water molecules can act either as a single-donor-single-acceptor, as a double-proton-donor, or as a double-donor-single-acceptor in both the firs1183t a1192nd the second solvation shell of the OH- ion core. Interconversion among the isomers appears to be rapid as manifested in the observed spectra dominated by broad and congested absorptions. To understand the nature of spectral broadening and congestion, systemic comparisons of the results are made against those of the corresponding protonated cations, H+(H₂O)_n|1 and the corresponding halide anions, X-(H²O)ⁿ X = F, Cl, Br, and I. It is suggested that the spectral complexities observed for OH-(H₂O)_4,5 are predominantly a result of sampling configurations with a large distribution of O_solvent-O_ion-O_solvent angles and O_solvent … H-O_solvent distances between water molecules in the firs1175t a1181nd/or second hydration shells, together with the existence of more than one isomer in the supersonic expanson and rapid isomeric interconversion among them.