Infrared Spectra of H+(H2O)5-8 Clusters: Evidence for Symmetric Proton Hydration
05 Feb 2000-Journal of the American Chemical Society (American Chemical Society)-Vol. 122, Iss: 7, pp 1398-1410
TL;DR: In this article, a vibrational predissociation spectroscopy and ab initio calculations of protonated water clusters from a supersonic expansion were performed at the B3LYP/6-31+G* level.
Abstract: Protonated water clusters, H+(H2O)n (n = 5−8), from a supersonic expansion have been investigated by vibrational predissociation spectroscopy and ab initio calculations. The experimental spectra were obtained at an estimated cluster temperature of 170 ± 20 K. Recorded absorption bands at the frequency range of 2700−3900 cm-1 are attributed to the free- and hydrogen-bonded-OH stretches of the ion core and the surrounding solvent molecules. Ab initio calculations, performed at the B3LYP/6-31+G* level, indicate that geometries of the H+(H2O)5-8 isomers are close in energy, with the excess proton either localized on a single water molecule, yielding H3O+(H2O)n-1, or equally shared by two molecules, yielding H5O2+(H2O)n-2. Systematic comparison of the experimental and computed spectra provides compelling evidence for both cases. The unique proton-transfer intermediate H5O2+(H2O)4 was identified, for the first time, by its characteristic bonded-OH stretching absorptions at 3178 cm-1. The existence of five-membe...
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TL;DR: This work reports how the vibrational spectrum of protonated water clusters evolves in the size range from 2 to 11 water molecules, revealing the pronounced spectral impact of subtle changes in the hydration environment.
Abstract: The ease with which the pH of water is measured obscures the fact that there is presently no clear molecular description for the hydrated proton. The mid-infrared spectrum of bulk aqueous acid, for example, is too diffuse to establish the roles of the putative Eigen (H 3 O + ) and Zundel (H 5 O 2 + ) ion cores. To expose the local environment of the excess charge, we report how the vibrational spectrum of protonated water clusters evolves in the size range from 2 to 11 water molecules. Signature bands indicating embedded Eigen or Zundel limiting forms are observed in all of the spectra with the exception of the three- and five-membered clusters. These unique species display bands appearing at intermediate energies, reflecting asymmetric solvation of the core ion. Taken together, the data reveal the pronounced spectral impact of subtle changes in the hydration environment.
714 citations
TL;DR: The OH stretching vibrational spectra of size-selected H+(H2O)n clusters through the region of the pronounced “magic number” at n = 21 in the cluster distribution provide direct evidence that, for the magic number cluster, all the dangling OH groups arise from water molecules in similar binding sites.
Abstract: We report the OH stretching vibrational spectra of size-selected H+(H2O)n clusters through the region of the pronounced “magic number” at n = 21 in the cluster distribution. Sharp features are observed in the spectra and assigned to excitation of the dangling OH groups throughout the size range 6 ≤ n ≤ 27. A multiplet of such bands appears at small cluster sizes. This pattern simplifies to a doublet at n = 11, with the doublet persisting up to n = 20, but then collapsing to a single line in the n = 21 and n = 22 clusters and reemerging at n = 23. This spectral simplification provides direct evidence that, for the magic number cluster, all the dangling OH groups arise from water molecules in similar binding sites.
542 citations
TL;DR: A comprehensive review of the thermochemistry and its structural implications obtained from ab initio calculations will be presented, and relevant recent results from spectroscopy will be illustrated.
Abstract: 1.1. Historical Background Hydrogen bonds1,2 are one of the principal intermolecular forces. A special class are ionic hydrogen bonds (IHBs) that form between ions and molecules with bonds strengths of 5-35 kcal/mol, up to a third of the strength of covalent bonds. These strong interactions are critical, for example, in ionic clusters and nucleation, in electrolytes, ion solvation, and acid-base chemistry, in the structures of ionic crystals, surfaces, silicates, and clays, in surface adsorption, and in self-assembly in supramolecular chemistry and molecular crystals.3 IHBs are also important in bioenergetics including protein folding, enzyme active centers, formation of membranes and proton transport, and biomolecular recognition. With such wide-ranging roles, the fundamental properties of IHB interactions need to be understood. The energetics of IHB interactions cannot be isolated and quantified in the condensed phase. However, these interactions can be isolated and studied quantitatively in gas phase. These studies lead to a fundamental understanding of relations between IHB bond strengths and molecular structure, the solvation of ions, especially in the critical inner shells, and acid-based phenomena and bioenergetics. This review will present the basic insights that have been obtained in the past four decades. It will present a comprehensive review of the thermochemistry and its structural implications obtained from ab initio calculations. Relevant recent results from spectroscopy will be also illustrated. The advent of variable temperature high-pressure mass spectrometry (HPMS) introduced by Field and co-workers in the 1960s4 and pulsed high-pressure mass spectrometry (PHPMS) introduced by Kebarle in the late 1960s5 have been particularly significant. These workers realized that at pressures of several torrs and gas densities of 1016-1017 cm-3 in ion sources, ions can undergo 103-106 collisions with neutral molecules during typical residence times of 0.1-10 ms and establish thermal ion populations and * E-mail: m.mautner@solis1.com. 213 Chem. Rev. 2005, 105, 213−284
538 citations
TL;DR: Size-dependent development of the hydrogen bond network structure in largesized clusters of protonated water, H+(H2O)n, was probed by infrared spectroscopy of OH stretches by demonstrating that the chain structures at small sizes develop into two-dimensional net structures and then into nanometer-scaled cages.
Abstract: Size-dependent development of the hydrogen bond network structure in largesized clusters of protonated water, H+(H2O)n (n = 4 to 27), was probed by infrared spectroscopy of OH stretches. Spectral changes with cluster size demonstrate that the chain structures at small sizes (n ≲ 10) develop into two-dimensional net structures (∼10
489 citations
TL;DR: It is demonstrated that enhancing the hydrability of the h-LAH could change the water state and partially activate the water, hence facilitating water evaporation, and raises the solar vapor generation to a record rate of ~3.6 kg m−2 hour−1 under 1 sun.
Abstract: Water purification by solar distillation is a promising technology to produce fresh water. However, solar vapor generation, is energy intensive, leading to a low water yield under natural sunlight. Therefore, developing new materials that can reduce the energy requirement of water vaporization and speed up solar water purification is highly desirable. Here, we introduce a highly hydratable light-absorbing hydrogel (h-LAH) consisting of polyvinyl alcohol and chitosan as the hydratable skeleton and polypyrrole as the light absorber, which can use less energy ( −2 hour −1 under 1 sun. The h-LAH-based solar still also exhibits long-term durability and antifouling functionality toward complex ionic contaminants.
475 citations
References
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TL;DR: In this paper, it is suggested that the molecular mechanism behind prototropic mobility involves a periodic series of isomerizations between H 9 O 4 + and H 5 O 2 +, the first trigerred by hyrdogen-bond cleavage of a second-shell water molecule and the second by the reverse, hydrogen-bonder formation process.
2,664 citations
TL;DR: In this article, the authors investigated the structure and proton transfer dynamics of the solvation complexes, which embed the ions in the network of hydrogen bonds in the liquid, and they showed that the entire structure of the charged complex migrates through the hydrogen bond network.
Abstract: Charge defects in water created by excess or missing protons appear in the form of solvated hydronium H3O+ and hydroxyl OH− ions. Using the method of ab initio molecular dynamics, we have investigated the structure and proton transfer dynamics of the solvation complexes, which embed the ions in the network of hydrogen bonds in the liquid. In our ab initio molecular dynamics approach, the interatomic forces are calculated each time step from the instantaneous electronic structure using density functional methods. All hydrogen atoms, including the excess proton, are treated as classical particles with the mass of a deuterium atom. For the H3O+ ion we find a dynamic solvation complex, which continuously fluctuates between a (H5O2)+ and a (H9O4)+ structure as a result of proton transfer. The OH− has a predominantly planar fourfold coordination forming a (H9O5)− complex. Occasionally this complex is transformed in a more open tetrahedral (H7O4)− structure. Proton transfer is observed only for the more waterlike (H7O4)− complex. Transport of the charge defects is a concerted dynamical process coupling proton transfer along hydrogen bonds and reorganization of the local environment. The simulation results strongly support the structural diffusion mechanism for charge transport. In this model, the entire structure—and not the constituent particles—of the charged complex migrates through the hydrogen bond network. For H3O+, we propose that transport of the excess proton is driven by coordination fluctuations in the first solvation shell (i.e., second solvation shell dynamics). The rate‐limiting step for OH− diffusion is the formation of the (H7O4)− structure, which is the solvation state showing proton transfer activity.
762 citations
698 citations
TL;DR: In this paper, a two color laser scheme consisting of a tunable cw infrared laser with 0.5 cm^−1 resolution used to excite the O−H stretching vibrations and a cw CO2 laser that dissociates the vibrationally excited cluster ion through a multiphoton process is presented.
Abstract: The gas phase infrared spectra of the hydrated hydronium cluster ions H3O+·(H2O)n(n=1, 2, 3) have been observed from 3550 to 3800 cm^−1. The new spectroscopic method developed for this study is a two color laser scheme consisting of a tunable cw infrared laser with 0.5 cm^−1 resolution used to excite the O–H stretching vibrations and a cw CO2 laser that dissociates the vibrationally excited cluster ion through a multiphoton process. The apparatus is a tandem mass spectrometer with a radio frequency ion trap that utilizes the following scheme: the cluster ion to be studied is first mass selected; spectroscopic interrogation then occurs in the radio frequency ion trap; finally, a fragment ion is selected and detected using ion counting techniques. The vibrational spectra obtained in this manner are compared with that taken previously using a weakly bound H2 "messenger." A spectrum of H7 O + 3 taken using a neon messenger is also presented. Ab initio structure and frequency predictions by Remington and Schaefer are compared with the experimental results.
459 citations
TL;DR: In this paper, the hydrogen-bonding topology of two conformers of the benzene-(water) 8 cluster was characterized using Resonant Two-photon ionization, ultraviolet hole burning, and resonant ion-dip infrared (RIDIR) spectroscopy.
Abstract: Resonant two-photon ionization, ultraviolet hole-burning, and resonant ion-dip infrared (RIDIR) spectroscopy were used to assign and characterize the hydrogen-bonding topology of two conformers of the benzene-(water) 8 cluster. In both clusters, the eight water molecules form a hydrogen-bonded cube to which benzene is surface-attached. Comparison of the RIDIR spectra with density functional theory calculations is used to assign the two (water) 8 structures in benzene-(water) 8 as cubic octamers of D 2 d and S 4 symmetry, which differ in the configuration of the hydrogen bonds within the cube. OH stretch vibrational fundamentals near 3550 wave numbers provide unique spectral signatures for these “molecular ice cubes.”
421 citations