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Single charge transfer reactions in the collision of ions at a laboratory energy of 2 keV with N 2 were observed using translational energy spectroscopy (TES). Within the limitation of the energy analyser resolution (∼ 8/ q eV, q being the ionic charge number), the translational energy spectrum shows a single broad charge transfer peak with a rich substructure. The latter looks like a conglomeration of closely spaced channels clumped together, corresponding mainly to charge transfer into excited states , rather than into the ground state. The reaction channel assignments were made using data available in the literature. Our findings are in accord with a recent experimental result, but there are no theoretical calculations to compare our experimental measurements with. [ABSTRACT FROM AUTHOR]

Starting with H[SUP+][CH[SUB3]C(O)CH[SUB2]C(O)CH[SUB3]] (denoted H[SUP+]PD), the protonated diketone-water clusters H[SUP+]PD(H[SUB2]O)[SUBn] (n = 1-3) have been characterized by density functional theory calculations in combination with vibrational predissociation spectroscopy to explore the conformational changes of a protonated bifunctional ion solvated by water in the gas phase. Theoretical calculations for H[SUP+]PD revealed that the ion contains an intramolecular hydrogen bond (IHB), with two oxygen atoms bridged by the extra proton in an O-H[SUP+] ... O form. Attachment of one water molecule to it readily ruptures this IHB, replacing the H[SUP+] by the H[SUB3]O[SUP+] moiety. Further replacement of the IHB by two water molecules occurs at n = 2 and the -C(O)CH[SUB2]C(O)- chain is fully opened (or unfolded) after transfer of the extra proton to the water trimer at n = 3. To verify the computational findings, infrared spectroscopic measurements were performed using a vibrational predissociation ion trap spectrometer to identify cluster isomers from the signatures of hydrogen bonded and non-hydrogen bonded OH stretching spectra of H[SUP+]PD(H[SUB2]O)[SUB2,3] produced in a corona discharge supersonic expansion. Besides open form isomers, evidence for the formation of water-bridged structures has been found for H[SUP+]PD(H[SUB2]O)[SUB3] at an estimated temperature of 200 K. A detailed illustration of the unfolding steps as well as the energy profiles for the evolution of a two-water bridge isomer from the protonated H[SUP+]PD monomer are analysed pictorially including both stable intermediates and transition states in the present investigation. [ABSTRACT FROM AUTHOR]

Size-selected hydroxide ion water tetramers and pentamers [OH[sup -] (H[sub 2]O)[sub 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 2650-3850cm [sup -1] show some broad absorption bands attributed to the free and hydrogen bonded OH stretches of OH[sup -] (H[sub 2]O)[sub 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[sup -] (H[sub 2]O)[sub 4] and OH (H[sub 2]O)[sub 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 first and 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[sup +](H[sub 2]O)[sub n+1] and the corresponding halide anions, X[sup -] (H[sub 2]O)[sub n], X = F, Cl, Br, and I. It is suggested that the spectral complexities observed for OH[sup -](H[sub 2]O)[sub 4,5] are predominantly a result of sampling configurations with a large distribution of O[sub solvent]-O[sub ion]-O[sub solvent] angles and O[sub solvent] · · · H-O[sub solvent] distances between water molecules in the first and/or second hydration shells, together with the existence of more than one isomer in the supersonic expanson and rapid isomeric interconversion among them. [ABSTRACT FROM AUTHOR]