Hydronium Cation Research Articles

Deciphering the reaction between a hydrated electron and a hydronium ion at elevated temperatures

The formation of a H˙ atom in liquid water from the reaction of a hydrated electron with a hydronium cation is a very challenging subject in chemical processes. Here picosecond pulse radiolysis measurements are performed at elevated temperatures, up to 350 °C, of acidic H2O and D2O solutions (up to 0.1 mol L(-1) HClO4) with the aim of investigating several issues related to this reaction. First, the red shift of the solvated electron absorption band in D2O with increasing temperature is found to be affected by the presence of D3O(+) in solution. The modified absorption spectra demonstrate the formation of a transient pair between D3O(+) and solvated electrons at elevated temperature (200-250 °C) when the concentration of D3O(+) is higher than 0.05 mol L(-1). For higher temperatures at 300 and 350 °C when the rate constant is almost diffusion controlled, the pair is no longer observable. Second, the presolvated electron in D2O is not scavenged up to 250 °C in solution containing 0.1 mol L(-1) D3O(+). Third, the decays in the picosecond range obtained under different conditions show that the rate constants are strongly affected by the temperature and by ionic strength. The model with an equation of log(k/k0) = 2A(I)(0.5)/1 + b(I)(0.5) gives a good fit of the experimental results by taking into account the variation of ionic strength, I, and, in particular, by considering the temperature dependence of the constant A.

Direct Evidence for Transient Pair Formation between a Solvated Electron and H3O(+) Observed by Picosecond Pulse Radiolysis.

The reaction between the solvated electron and hydronium cation H3O(+) in water constitutes a fundamental reaction in chemistry. Due to significant rearrangement of solvent molecules around both the electron and H3O(+), the reaction rate of this process is not controlled by diffusion. The presence of a reaction barrier suggests the formation of an intermediate that has so far not been observed. Here, the time-resolved visible absorption spectra in three concentrated acid solutions, perchloric, sulfuric, and phosphoric, at various concentrations are recorded by the picosecond pulse radiolysis method. In contrast to previous reports, a strong blue shift of the absorption band of the solvated electron in acidic solutions compared to neat water is clearly observed, consistent with formation of a pair between the solvated electron and hydronium cation.

Photoionization and fragmentation of H3O+under XUV irradiation

The photolysis of the hydronium cation H${}_{3}$O${}^{+}$ has been studied at the extreme ultraviolet wavelengths of $35.56\ifmmode\pm\else\textpm\fi{}0.24$ nm ($34.87\ifmmode\pm\else\textpm\fi{}0.24$ eV) and $21.85\ifmmode\pm\else\textpm\fi{}0.17$ nm ($56.74\ifmmode\pm\else\textpm\fi{}0.44$ eV) using a crossed ion-photon beam setup at the free-electron laser FLASH. Coincidence photoelectron and photofragment spectroscopy was performed at 21.85 nm, where both inner and outer valence ionization are allowed, and revealed that the XUV photolysis of H${}_{3}$O${}^{+}$ is by far dominated by ionization of outer valence electrons forming the ${}^{1}{A}_{1}$ and ${}^{2}E$ states of the dication H${}_{3}$O${}^{2+}$. The dications were found to dissociate into the channels H${}_{2}$O${}^{+}$+H${}^{+}$ ($72\ifmmode\pm\else\textpm\fi{}4%$), OH${}^{0}$+2H${}^{+}$ ($18\ifmmode\pm\else\textpm\fi{}6%$), and OH${}^{+}$+H${}^{+}$+H${}^{0}$ ($10\ifmmode\pm\else\textpm\fi{}1%$). A kinematic analysis of the H${}_{2}$O${}^{+}$+H${}^{+}$ channel after photoabsorption at 35.56 nm (where only outer valence ionization is possible) showed dissociation into excited states of the water radical ion, where the ${}^{1}{A}_{1}$ state breaks up into the linear $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{A}{\phantom{\rule{0.16em}{0ex}}}^{2}{A}_{1}$ state of H${}_{2}$O${}^{+}$ and the ${}^{2}E$ state decays into the strongly bent $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{B}{\phantom{\rule{0.16em}{0ex}}}^{2}{B}_{2}$ state. Finally, from the ${}^{2}E$ state of H${}_{3}$O${}^{2+}$, dissociation into OH${}^{0}(X{\phantom{\rule{0.16em}{0ex}}}^{2}\ensuremath{\Pi}$)+2H${}^{+}$ was identified to occur with a near linear dissociation geometry.

Dynamics and structural changes of small water clusters on ionization

Despite utmost importance in understanding water ionization process, reliable theoretical results of structural changes and molecular dynamics (MD) of water clusters on ionization have hardly been reported yet. Here, we investigate the water cations [(H2O)(n = 2-6)(+)] with density functional theory (DFT), Möller-Plesset second-order perturbation theory (MP2), and coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)]. The complete basis set limits of interaction energies at the CCSD(T) level are reported, and the geometrical structures, electronic properties, and infrared spectra are investigated. The characteristics of structures and spectra of the water cluster cations reflect the formation of the hydronium cation moiety (H3O(+)) and the hydroxyl radical. Although most density functionals fail to predict reasonable energetics of the water cations, some functionals are found to be reliable, in reasonable agreement with high-level ab initio results. To understand the ionization process of water clusters, DFT- and MP2-based Born-Oppenheimer MD (BOMD) simulations are performed on ionization. On ionization, the water clusters tend to have an Eigen-like form with the hydronium cation instead of a Zundel-like form, based on reliable BOMD simulations. For the vertically ionized water hexamer, the relatively stable (H2O)5(+) (5sL4A) cluster tends to form with a detached water molecule (H2O).

Unrestricted absolutely localized molecular orbitals for energy decomposition analysis: Theory and applications to intermolecular interactions involving radicals

Radical-closed shell and radical-radical intermolecular interactions are less well-understood than those between closed shell species. With the objective of gaining additional insight, this work reports a generalization of the absolutely localized molecular orbital (ALMO) energy decomposition analysis (EDA) to open shell fragments, described by self-consistent field methods, such as standard density functional theory. The ALMO-EDA variationally partitions an intermolecular interaction energy into three separate contributions; frozen orbital interactions, polarization, and charge transfer. The first examples involve comparison of the interactions of alkanes and alkyl radicals (methyl radical, methane, tertiary butyl radical, and isobutane) with sodium, potassium, hydronium, and ammonium cations. A second series of examples involve benzene cation interacting with a series of nucleophiles in both on-top and side-on geometries. The ALMO-EDA yields a variety of interesting insights into the relative roles of its component contributions as the interacting partners and their geometries are changed.

Dihydronium tetrachromate(VI), (H3O)2Cr4O13

The crystal structure of (H3O)2Cr4O13 is isotypic with K2Cr4O13. The finite tetra­chromate anion in the title structure consists of four vertex-sharing CrO4 tetra­hedra and exhibits a typical zigzag arrangement. The crystal packing is stabilized by hydrogen bonds between these anions and hydro­nium cations. The two different hydro­nium cations are surrounded by nine O atoms of tetra­chromate anions, with O⋯O distances ranging between 2.866 (8) and 3.282 (7) Å.

SO2 Hydrolysis: Ab initio MD Study of the Formation of Bisulfite Ion

Ab initio molecular dynamics simulations have been performed to study the dissolution of SO2 in water. It has been obtained that the hydrated SO2 is surrounded by the water molecules without any S-H hydrogen bond, restraining the sulfonate anion formation but allowing the bisulfite isomer formation. The metadynamics method has been employed to explore the free energy surface of the SO2 + H2O reaction. The simulations revealed that the hydrated SO2 forms bisulfite anion and hydronium cation after overcoming a ca. 17 kcal/mol free energy barrier. Direct, one-step H2SO3 formation could not been observed, in sharp contrast with earlier cluster calculations. These findings indicate a step-wise H2SO3 formation in water. The presence of the sulfur lone pair represents an important constraint on the mechanism: the nucleophilic H2O attack can occur only from certain angles as shown by the reactive trajectories.

Theory of collective proton motion at interfaces with densely packed protogenic surface groups

We present a theoretical study of collective proton transport at a 2D array of end-grafted protogenic surface groups with sulfonic acid head groups. The graft positions of the surface groups form a regular hexagonal lattice. We consider the interfacial array at a high packing density of the surface groups and under minimal hydration with one water molecule added per head group. For these conditions, the stable interfacial conformation consists of a bicomponent lattice of hexagonally ordered sulfonate anions and interstitial hydronium cations. Hydronium ion motion occurs as a travelling solitary wave. We analyse the microscopic parameters of the solitons and study the influence of different potential profiles on the proton motion created by rotation and tilting of sidechains and sulfonate anions. Using soliton solutions of the equation of motion, we establish relations between the energy and mobility of the solitons and the microscopic structural and interaction parameters of the array.

Computational Study of the Hydration of Sulfuric Acid Dimers: Implications for Acid Dissociation and Aerosol Formation

We have investigated the thermodynamics of sulfuric acid dimer hydration using ab initio quantum mechanical methods. For (H(2)SO(4))(2)(H(2)O)(n) where n = 0-6, we employed high-level ab initio calculations to locate the most stable minima for each cluster size. The results presented herein yield a detailed understanding of the first deprotonation of sulfuric acid as a function of temperature for a system consisting of two sulfuric acid molecules and up to six waters. At 0 K, a cluster of two sulfuric acid molecules and one water remains undissociated. Addition of a second water begins the deprotonation of the first sulfuric acid leading to the di-ionic species (the bisulfate anion HSO(4)(-), the hydronium cation H(3)O(+), an undissociated sulfuric acid molecule, and a water). Upon the addition of a third water molecule, the second sulfuric acid molecule begins to dissociate. For the (H(2)SO(4))(2)(H(2)O)(3) cluster, the di-ionic cluster is a few kcal mol(-1) more stable than the neutral cluster, which is just slightly more stable than the tetra-ionic cluster (two bisulfate anions, two hydronium cations, and one water). With four water molecules, the tetra-ionic cluster, (HSO(4)(-))(2)(H(3)O(+))(2)(H(2)O)(2), becomes as favorable as the di-ionic cluster H(2)SO(4)(HSO(4)(-))(H(3)O(+))(H(2)O)(3) at 0 K. Increasing the temperature favors the undissociated clusters, and at room temperature we predict that the di-ionic species is slightly more favorable than the neutral cluster once three waters have been added to the cluster. The tetra-ionic species competes with the di-ionic species once five waters have been added to the cluster. The thermodynamics of stepwise hydration of sulfuric acid dimer is similar to that of the monomer; it is favorable up to n = 4-5 at 298 K. A much more thermodynamically favorable pathway forming sulfuric acid dimer hydrates is through the combination of sulfuric acid monomer hydrates, but the low concentration of sulfuric acid relative to water vapor at ambient conditions limits that process.

The hydrolysis kinetics of monobasic and dibasic aminoalkyl esters of ketorolac

Six aminoethyl and aminobutyl esters of ketorolac containing 1-methylpiperazine (MPE and MPB), N-acetylpiperazine (APE and APB) or morpholine (ME and MB), were synthesized and their hydrolysis kinetics were studied. The hydrolysis was studied at pH 1 to 9 (for MPE, APE and ME) and pH 1 to 8 (for MPB, APB and MB) in aqueous phosphate buffer (0.16 M) with ionic strength (0.5 M) at 37°C. Calculation of kobs, construction of the pH-rate profiles and determination of the rate equations were performed using KaleidaGraph® 4.1. The hydrolysis displays pseudo-first order kinetics and the pH-rate profiles shows that the aminobutyl esters, MPE, APB and MB, are the most stable. The hydrolysis of the ethyl esters MPE, APE and ME, depending on the pH, is either fast and catalyzed by the hydroxide anion or slow and uncatalyzed for the diprotonated, monoprotonated and nonprotonated forms. The hydrolysis of the butyl esters showed a similar profile, albeit it was also catalyzed by hydronium cation. In addition, the hydroxide anion is 105 more effective in catalyzing the hydrolysis than the hydronium cation. The hydrolysis pattern of the aminoethyl esters is affected by the number and pKa of its basic nitrogen atoms. The monobasic APE and ME, show a similar hydrolysis pattern that is different than the dibasic MPE. The length of the side chain and the pKa of the basic nitrogen atoms in the aminoethyl moiety affect the mechanism of hydrolysis as the extent of protonation at a given pH is directly related to the pKa.

New structures of hydronium cation clusters.

Four new hydronium ion structures are investigated by means of quantum mechanical calculations at the DFT/B3LYP6-311+G(2d,2p) level of theory. There exist experimental crystallographic hydronium cations (H11O5 +) of two different geometrical structures, one BEXFEQ (acyclic) and one IYEPEH (cyclic). Molecular calculations reveal their relative stability. Another hydronium cation NEBDII (H15O7 +) when optimized reveals a totally new and unexpected structure. All three optimized structures are shown to be quite stable as judged by their binding energies, and therefore may possibly be found in solution. A main result of this article is the discovery of three new optimized structures of hydronium ions, all of which are preferentially ring structures. The optimized structure of H15O7 + is a cube lacking a vertex. Putting a water molecule at the "empty" vertex leads by energy optimization to a structure of H17O8 + which has the approximate symmetry of a cube. This cubic structure, as judged by its fragments, is one of the most interesting of the hydronium ions studied in this paper. The addition of H3O+ to a group of seven neutral molecules in the hypothetical reaction H3O+ + 7 H2O → H17O8 + induces two water molecules to each capture a proton at the expense of two other water molecules (converting them into hydroxyl anions) leading to a cluster with the formula , where the superscripts are the integrated QTAIM atomic charges (in atomic units) on the respective species (inside the bracket) or on groups of a given species (outside the bracket). The cubic arrangement of 3H3O+.3H2O.2OH- is accompanied with a significant redistribution of charge: Each hydronium cation carries ca. +0.7 au, the hydroxyl anions only around -0.6 au each, while the water molecules remain quasi-neutral with a slight positive charge.

Computational Study on a HS– Sensing Reaction Utilizing a Pyrylium Derivative

In this paper, we present a comprehensive computational study on the hydrogen sulfide sensing mechanism in aqueous solution using a pyrylium derivative. The possible sensing mechanisms were investigated under the neutral condition and acidic condition in the gas phase and in aqueous solution. The pyrylium-thiopyrylium transformation under the neutral condition is thermodynamically unfavorable, while it is greatly facilitated in the acidic condition catalyzed by a hydronium cation. In addition, the UV-vis absorption maxima of pyryliums and thiopyryliums were investigated at the TDDFT/B3LYP/6-31G+(d,p) level. The red shift of absorption maximum from unsubstituted pyrylium and thiopyrylium to dimethylamino-substituted pyrylium and thiopyrylium as well as the red shift seen in the pyrylium-thiopyrylium transformation is interpreted in terms of the molecular orbital theory.

Competitive Anion/Water and Cation/Water Interactions at Electrified Copper/Electrolyte Interfaces Probed by in Situ X-ray Diffraction

The full 3D structure of a copper/electrolyte interface is studied by means of in situ surface X-ray diffraction (SXRD) methods. Chloride anions chemisorb on Cu(100) in 10 mM HCl at high potentials under formation of a p(1 × 1)-Cl adlayer. This anionic chemisorption layer serves as a structural template for the lateral ordering of water molecules and hydronium cations in the near-surface liquid electrolyte. Evidence for this interfacial geometry is mainly derived from the intensity distribution of surface-sensitive X-ray diffraction data along the (10L)-adlayer rod. The characteristic oscillating intensity distribution along the (10L) rod is due to a centered bilayer system consisting of the anionic inner Helmholtz layer (IHL) of chemisorbed chloride and the cationic outer Helmholtz layer (OHL). The latter is constituted in the present case by hydronium cations that preferentially populate 4-fold hollow sites of the underlying chloride lattice. IHL and OHL are separated by an extra interfacial water layer...

Location of extra-framework Co2+, Ni2+, Cu2+ and Zn2+ cations in natural and dealuminated clinoptilolite

In the present work a combination of chemically constrained Rietveld refinement and computer simulation is used for the determination of the positions of the extra-framework cations Co2+, Ni2+, Cu2+ and Zn2+ in the channels of clinoptilolite. The analysis of the metal rich clinoptilolites with two different Si/Al ratio (4.7 and 7.8) demonstrates that most of the cations are located in two extra-framework sites, the first one in the center of channel A and the second one in the center of channel B. In the case of the Cu2+ exchanged zeolite with high Si/Al ratio (4.7), a third site is found. This site is located at 1.65Å of the center of the A channel and can be considered as a highly disordered first site. All the metal ions are coordinated to water molecules with no coordination to the zeolite framework. The presence of hydronium cations controls the relative occupancy of the transition metals in the observed sites.

Chasing charge localization and chemical reactivity following photoionization in liquid water

The ultrafast dynamics of the cationic hole formed in bulk liquid water following ionization is investigated by ab initio molecular dynamics simulations and an experimentally accessible signature is suggested that might be tracked by femtosecond pump-probe spectroscopy. This is one of the fastest fundamental processes occurring in radiation-induced chemistry in aqueous systems and biological tissue. However, unlike the excess electron formed in the same process, the nature and time evolution of the cationic hole has been hitherto little studied. Simulations show that an initially partially delocalized cationic hole localizes within ~30 fs after which proton transfer to a neighboring water molecule proceeds practically immediately, leading to the formation of the OH radical and the hydronium cation in a reaction which can be formally written as H(2)O(+) + H(2)O → OH + H(3)O(+). The exact amount of initial spin delocalization is, however, somewhat method dependent, being realistically described by approximate density functional theory methods corrected for the self-interaction error. Localization, and then the evolving separation of spin and charge, changes the electronic structure of the radical center. This is manifested in the spectrum of electronic excitations which is calculated for the ensemble of ab initio molecular dynamics trajectories using a quantum mechanics/molecular mechanics (QM∕MM) formalism applying the equation of motion coupled-clusters method to the radical core. A clear spectroscopic signature is predicted by the theoretical model: as the hole transforms into a hydroxyl radical, a transient electronic absorption in the visible shifts to the blue, growing toward the near ultraviolet. Experimental evidence for this primary radiation-induced process is sought using femtosecond photoionization of liquid water excited with two photons at 11 eV. Transient absorption measurements carried out with ~40 fs time resolution and broadband spectral probing across the near-UV and visible are presented and direct comparisons with the theoretical simulations are made. Within the sensitivity and time resolution of the current measurement, a matching spectral signature is not detected. This result is used to place an upper limit on the absorption strength and/or lifetime of the localized H(2)O(+) ((aq)) species.

Structural Effects on Water Adsorption on Gold Electrodes

We study the molecular properties of the interface formed between aqueous sulfuric acid solutions and gold electrodes by means of surface-enhanced infrared absorption spectroscopy (SEIRAS). The shape of the SEIRAS spectra is observed to be strongly dependent on the deposition rate with which the gold electrodes are prepared. We find that the water molecules coordinating to coadsorbed sulfate anions become invisible in the SEIRAS spectra when the gold films are deposited at 1 A/s, instead of the customary deposition rate of 0.1 A/s employed in previous studies. Atomic force microscopy images of the gold deposits demonstrate that the increase of the gold deposition rate produces a decrease in the size of the nanoparticles composing the gold films. This suggests that water molecules coadsorbed with sulfate anions on small gold nanoparticles are oriented parallel to the surface. On the other hand, the fact that these water molecules are not detected by SEIRAS facilitates the study of the adsorption of hydronium cations, since these SEIRAS bands overlap. It is concluded that the adsorption of sulfate anions does not involve the coadsorption of any hydronium-water complex, since the SEIRAS band of the latter species exhibits a steady decrease with increasing potential

Water trimer cation

By using density functional theory (DFT) and high-level ab initio theory, we have investigated the structure, interaction energy, electronic property, and IR spectra of the water trimer cation [(H2O) 3 + ]. Two structures of the water trimer cation [the H3O+ containing linear (3Lp) structure versus the ring (3OO) structure] are compared. For the complete basis set (CBS) limit of coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)], the 3Lp structure is 11.9 kcal/mol more stable than the 3OO structure. This indicates that the ionization of water clusters produce the hydronium cation moiety (H3O+) and the hydroxyl radical. It is interesting to note that the calculation results of the water trimer cation vary seriously depending on the calculation level. At the level of Moller–Plesset second-order perturbation (MP2) theory, the stability of 3OO is underestimated due to the underestimated O…O hemibonding energy. This stability is also underestimated even for the CCSD(T) single point calculations on the MP2-optimized geometry. For the 3OO structure, the MP2 and CCSD(T) calculations give closed-ring structures with a hemi-bond between two O atoms, while the DFT calculations show open-ring structures due to the overestimated O…O hemibonding energy. Thus, in order to obtain reliable stabilities and frequencies of the water trimer cation, the CCSD(T) geometry optimizations and frequency calculations are necessary. In this regard, the DFT functionals need to be improved to take into account the proper O…O hemibonding energy.

Molecular Dynamics Simulation of Sum Frequency Generation Spectra of Aqueous Sulfuric Acid Solution

The surface structure of aqueous sulfuric acid solution at 0.02x (x is the mole fraction) concentration is investigated by molecular dynamics (MD) simulation with newly developed flexible and polarizable molecular models. The models are applied to calculate the SFG spectrum on the assumption that the acid dissociation of sulfuric acid at the surface is the same as in the bulk. The calculated SFG spectrum well reproduces the experimental one, indicating that the assumption on the acid dissociation is valid in a relatively low concentration range. The density profiles of the constituent ions at the surface region show distinct surface preference in the order of the hydronium cation, bisulfate anion, and sulfate dianion, which thereby forms an electric double layer and strongly perturbs the orientational structure of surface water. The enhancement of the SFG intensity at the hydrogen-bonding OH stretching region and the depletion at the dangling (free) OH region are elucidated from the interfacial structure.

Synthesis, tautomeric forms, specific intermolecular interactions, and lipophilicity of methylated 6-hydroxypyridazine-3-carboxylic acid and its 4,5-dihydro analogs

Effects of methylation for intermolecular interactions and lipophilicity have been studied for a series of methylated 4,5-dihydro-6-hydroxypyridazine-3-carboxylic and 6-hydroxypyridazine-3-carboxylic acids ( 1 and 2). In solution they exist in equilibrium of the lactam and lactim tautomers, with the reverse preferences for analogs 1 and 2, which affect the syntheses of their methylated derivatives. Carboxylic acid 2 preferably crystallizes as a hydrate, built of carboxylate anions and hydronium cations 2 − H 3O +, hydrogen bonded into catemeric patterns involving both ions. In methyl 4,5-dihydro-6-oxopyridazine-3-carboxylate ( 4A) the molecules are NH⋯O hydrogen bonded into chains. In both structures 2 − H 3O + and 4A, there are relatively strong CH⋯O hydrogen bonds, arranging the molecules into sheets. The increased lipophilicity of the methylated derivatives has been correlated with the formation of CH⋯O bonds.

Crown Ether Complexes with H3O+ and NH4+: Proton Localization and Proton Bridge Formation

The complexes formed by crown ethers with hydronium and ammonium cations are of key relevance for the understanding of their supramolecular behavior in protic solvents. In this work, the complexes of the 15-crown-5 (15c5) and 18-crown-6 (18c6) ethers with H₃O⁺ and NH₄⁺ and their deuterated variants are investigated under isolated conditions. The study employs infrared multiple photon dissociation (IRMPD) vibrational spectroscopy and DFT B3LYP/6-31++G(d,p) calculations for conformational assignment. The 18c6 ether provides two energetically nearby C(3v) conformations with commensurate linear O-H···O and N-H···O bonds. The 15c5 ether ring adopts partially folded asymmetric pyramidal geometries, yielding one shorter linear H bond and two longer non-linear H bonds. Remarkably, an appreciable broadening of the IRMPD vibrational bands is observed for the 15c5-H₃O⁺/D₃O⁺ complexes. This can be interpreted as a signature for partial sharing of the proton (or deuteron) between the water and the crown ether along the linear O-H···O intermolecular H bond, which is indeed particularly short for this complex.