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The (HCOOH) 2 anion, formed by electron attachment to the formic acid dimer (FA 2), is an archetypal system for exploring the mechanics of the electron-induced proton transfer motif that is purported to occur when neutral nucleic acid base-pairs accommodate an excess electron K. Aflatooni, G. A. Gallup, and P. D. Burrow, J. Phys. Chem. A 102, 6205 (1998)10.1021/jp980865n; J. H. Hendricks, S. A. Lyapustina, H. L. de Clercq, J. T. Snodgrass, and K. H. Bowen, J. Chem Phys. 104, 7788 (1996)10.1063/1.471484; C. Desfrancois, H. Abdoul-Carime, and J. P. Schermann, J. Chem Phys. 104, 7792 (1996). The FA 2 anion and several of its HD isotopologues were isolated in the gas phase and characterized using Ar-tagged vibrational predissociation and electron autodetachment spectroscopies. The photoelectron spectrum of the FA 2 anion was also recorded using velocity-map imaging. The resulting spectroscopic information verifies the equilibrium FA 2- geometry predicted by theory which features a symmetrical, double H-bonded bridge effectively linking together constituents that most closely resemble the formate ion and a dihydroxymethyl radical. The spectroscopic signatures of this ion were analyzed with the aid of calculated anharmonic vibrational band patterns. © 2012 American Institute of Physics.

The (HCOOH) 2 anion, formed by electron attachment to the formic acid dimer (FA 2), is an archetypal system for exploring the mechanics of the electron-induced proton transfer motif that is purported to occur when neutral nucleic acid base-pairs accommodate an excess electron K. Aflatooni, G. A. Gallup, and P. D. Burrow, J. Phys. Chem. A 102, 6205 (1998)10.1021/jp980865n; J. H. Hendricks, S. A. Lyapustina, H. L. de Clercq, J. T. Snodgrass, and K. H. Bowen, J. Chem Phys. 104, 7788 (1996)10.1063/1.471484; C. Desfrancois, H. Abdoul-Carime, and J. P. Schermann, J. Chem Phys. 104, 7792 (1996). The FA 2 anion and several of its HD isotopologues were isolated in the gas phase and characterized using Ar-tagged vibrational predissociation and electron autodetachment spectroscopies. The photoelectron spectrum of the FA 2 anion was also recorded using velocity-map imaging. The resulting spectroscopic information verifies the equilibrium FA 2- geometry predicted by theory which features a symmetrical, double H-bonded bridge effectively linking together constituents that most closely resemble the formate ion and a dihydroxymethyl radical. The spectroscopic signatures of this ion were analyzed with the aid of calculated anharmonic vibrational band patterns. © 2012 American Institute of Physics.

Many chemical reactions in atmospheric aerosols and bulk aqueous environments are influenced by the surrounding solvation shell, but the precise molecular interactions underlying such effects have rarely been elucidated. We exploited recent advances in isomer-specific cluster vibrational spectroscopy to explore the fundamental relation between the hydrogen (H)-bonding arrangement of a set of ion-solvating water molecules and the chemical activity of this ensemble. We find that the extent to which the nitrosonium ion (NO+) and water form nitrous acid (HONO) and a hydrated proton cluster in the critical trihydrate depends sensitively on the geometrical arrangement of the water molecules in the network. Theoretical analysis of these data details the role of the water network in promoting charge derealization.

Many chemical reactions in atmospheric aerosols and bulk aqueous environments are influenced by the surrounding solvation shell, but the precise molecular interactions underlying such effects have rarely been elucidated. We exploited recent advances in isomer-specific cluster vibrational spectroscopy to explore the fundamental relation between the hydrogen (H)-bonding arrangement of a set of ion-solvating water molecules and the chemical activity of this ensemble. We find that the extent to which the nitrosonium ion (NO+) and water form nitrous acid (HONO) and a hydrated proton cluster in the critical trihydrate depends sensitively on the geometrical arrangement of the water molecules in the network. Theoretical analysis of these data details the role of the water network in promoting charge derealization.

Predissociation spectra of the H5 O2+ ·R Gn (RG=Ar,Ne) cluster ions are reported in energy regions corresponding to both the OH stretching (3350-3850 cm-1) and shared proton (850-1950 cm-1) vibrations. The two free OH stretching bands displayed by the Ne complex are quite close to the band origins identified earlier in bare H5 O2+ [L. I. Yeh, M. Okumura, J. D. Myers, J. M. Price, and Y. T. Lee, J. Chem. Phys. 91, 7319 (1989)], indicating that the symmetrical H5 O2+ "Zundel" ion remains largely intact in H5 O2+ ·Ne. The low-energy spectrum of the Ne complex is simpler than that observed previously for H5 O2+ ·Ar, and is dominated by two sharp transitions at 928 and 1047 cm-1, with a weaker feature at 1763 cm-1. The H5 O2+ · Arn, n=1-5 spectra generally exhibit complex band structures reflecting solvent-induced symmetry breaking of the Zundel core ion. The extent of solvent perturbation is evaluated with electronic structure calculations, which predict that the rare gas atoms should attach to the spectator OH groups of H5 O2+ rather than to the shared proton. In the asymmetric complexes, the shared proton resides closer to the more heavily solvated water molecule, leading to redshifts in the rare gas atom-solvated OH stretches and to blueshifts in the shared proton vibrations. The experimental spectra are compared with recent full-dimensional vibrational calculations (diffusion Monte Carlo and multimode/vibrational configuration interaction) on H5 O2+. These results are consistent with assignment of the strong low-energy bands in the H5 O2+ ·Ne spectrum to the vibration of the shared proton mostly along the O-O axis, with the 1763 cm-1 band traced primarily to the out-of-phase, intramolecular bending vibrations of the two water molecules. © 2005 American Institute of Physics.

Predissociation spectra of the H5 O2+ ·R Gn (RG=Ar,Ne) cluster ions are reported in energy regions corresponding to both the OH stretching (3350-3850 cm-1) and shared proton (850-1950 cm-1) vibrations. The two free OH stretching bands displayed by the Ne complex are quite close to the band origins identified earlier in bare H5 O2+ [L. I. Yeh, M. Okumura, J. D. Myers, J. M. Price, and Y. T. Lee, J. Chem. Phys. 91, 7319 (1989)], indicating that the symmetrical H5 O2+ "Zundel" ion remains largely intact in H5 O2+ ·Ne. The low-energy spectrum of the Ne complex is simpler than that observed previously for H5 O2+ ·Ar, and is dominated by two sharp transitions at 928 and 1047 cm-1, with a weaker feature at 1763 cm-1. The H5 O2+ · Arn, n=1-5 spectra generally exhibit complex band structures reflecting solvent-induced symmetry breaking of the Zundel core ion. The extent of solvent perturbation is evaluated with electronic structure calculations, which predict that the rare gas atoms should attach to the spectator OH groups of H5 O2+ rather than to the shared proton. In the asymmetric complexes, the shared proton resides closer to the more heavily solvated water molecule, leading to redshifts in the rare gas atom-solvated OH stretches and to blueshifts in the shared proton vibrations. The experimental spectra are compared with recent full-dimensional vibrational calculations (diffusion Monte Carlo and multimode/vibrational configuration interaction) on H5 O2+. These results are consistent with assignment of the strong low-energy bands in the H5 O2+ ·Ne spectrum to the vibration of the shared proton mostly along the O-O axis, with the 1763 cm-1 band traced primarily to the out-of-phase, intramolecular bending vibrations of the two water molecules. © 2005 American Institute of Physics.