Proton Motion Research Articles

Phase with pressure-induced shuttlewise deformation in dense solid atomic hydrogen

A phase which shows pressure-induced shuttlewise structural deformation between orthorhombic $Fddd$ and tetragonal $I{4}_{1}/amd$ structures has been predicted in solid atomic hydrogen by means of the first-principles calculations, including harmonic zero-point energy contributions of proton motions. The $Fddd$ structure is formed by shear distortion from the $I{4}_{1}/amd$ structure, and the angle specifying the distortion changes with pressure in the range $84--{96}^{\ensuremath{\circ}}$ around ${90}^{\ensuremath{\circ}}$, which corresponds to $I{4}_{1}/amd$. In the shuttlewise deforming phase, the electron-phonon interaction is enhanced owing to phonon softenings, which brings about superconductivity at elevated temperatures.

Probing microphase separation and proton transport cooperativity in polymer‐tethered 1H‐tetrazoles

ABSTRACTTo elucidate the driving forces for phase separation and proton conductivity in polystyrenic alkoxy 1H‐tetrazole (PS‐Tet), an analogous polystyrenic alkoxy carboxylic acid (PS‐HA) was synthesized and the conductivity and chain dynamics of both materials measured. Proton and polymer motions illustrate dramatic differences in the nonaqueous behavior of carboxylic acids and 1H‐tetrazoles, belying similarities in their aqueous properties. Exceptional interactions between 1H‐tetrazoles drive phase separation not observed in PS‐HA or reported for other azole‐containing homopolymers. PS‐HA and PS‐Tet exhibit both dry (0% relative humidity) and hydrated proton dissociations proportional to their aqueous pKas, with residual water acting as the proton acceptor in both polymers. While water is the sole contributor to mobility in PS‐HA, PS‐Tet exhibits dynamic interactions with water allowing 1H‐tetrazole moieties to contribute to proton conduction even in the hydrated state. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1375–1387

Core-level transient absorption spectroscopy as a probe of electron hole relaxation in photoionized H+(H2O)n.

There is fundamental interest in understanding the coupled nuclear and electronic dynamics associated with charge transfer processes in complex molecules and materials, which are often mediated by electron, electron hole or proton motion. With dramatic improvements in the techniques to generate extreme ultraviolet (XUV) and X-ray femtosecond pulses, it now becomes possible to trigger and probe these kinds of processes in real time. Here we study the dynamics of an electron hole created by photoionization in the valence shell of protonated water clusters H(+)(H(2)O)(n). We demonstrate that the electron hole is strongly correlated with the protons forming the hydrogen bond network. We show that it is possible to probe key aspects of the valence electron hole dynamics and the coupled nuclear motion with femtosecond time resolution by resonantly exciting K-shell 1s electrons to fill the electron hole. This represents an opportunity for X-ray transient absorption spectroscopy.

Proton conduction in biopolymer exopolysaccharide succinoglycan

Protonic currents play a vital role in electrical signalling in living systems. It has been suggested that succinoglycan plays a specific role in alfalfa root nodule development, presumably acting as the signaling molecules. In this regard, charge transport and proton dynamics in the biopolymer exopolysaccharide succinoglycan have been studied by means of electrical measurements and nuclear magnetic resonance (NMR) spectroscopy. In particular, a dielectric dispersion in the system has revealed that the electrical conduction is protonic rather electronic. Besides, our laboratory- and rotating-frame 1H NMR measurements have elucidated the nature of the protonic conduction, activation of the protonic motion being associated with a glass transition.

The onset of ion heating during magnetic reconnection with a strong guide field

The onset of the acceleration of ions during magnetic reconnection is explored via particle-in-cell simulations in the limit of a strong ambient guide field that self-consistently and simultaneously follow the motions of protons and α particles. Heating parallel to the local magnetic field during reconnection with a guide field is strongly reduced compared with the reconnection of anti-parallel magnetic fields. The dominant heating of thermal ions during guide field reconnection results from pickup behavior of ions during their entry into reconnection exhausts and dominantly produces heating perpendicular rather than parallel to the local magnetic field. Pickup behavior requires that the ion transit time across the exhaust boundary (with a transverse scale of the order of the ion sound Larmor radius) be short compared with the ion cyclotron period. This translates into a threshold in the strength of reconnecting magnetic field that favors the heating of ions with high mass-to-charge. A simulation with a broad initial current layer produces a reconnecting system in which the amplitude of the reconnecting magnetic field just upstream of the dissipation region increases with time as reconnection proceeds. The sharp onset of perpendicular heating when the pickup threshold is crossed is documented. A comparison of the time variation of the parallel and perpendicular ion heating with that predicted based on the strength of the reconnecting field establishes the scaling of ion heating with ambient parameters both below and above the pickup threshold. The relevance to observations of ion heating in the solar corona is discussed.

Phase transition originating from order-disorder transformations of carboxy oxygen atoms coupled with dynamic proton motions in [PhCH2 NH(CH3)2]2 C2O4⋅H2 C2O4.

A new molecular phase transition material, [PhCH(2) NH(CH(3))(2)](2) C(2)O(4)⋅H(2)C(2)O(4), which undergoes a reversible phase transition at 151.6 K, has been successfully synthesized. Differential scanning calorimetry (DSC), specific heat capacity, and dielectric measurements confirm its reversible phase transition with a large thermal hysteresis of 15.1 K, demonstrating that the phase transition is typical first order. Variable-temperature single-crystal X-ray diffraction analyses reveal that the order-disorder transformations of carboxy oxygen atoms induce the structural phase transition. A slight reorientation of the oxalic acid unit is discovered to accompany the ordering of carboxy oxygen atoms at low temperature. The DSC measurement result of the deuterated analog is different to that of 1, indicating that proton dynamic motions in hydrogen bonds also contribute to the phase transition.

Solvent-induced red-shifts for the proton stretch vibrational frequency in a hydrogen-bonded complex. 1. A valence bond-based theoretical approach.

A theory is presented for the proton stretch vibrational frequency νAH for hydrogen (H-) bonded complexes of the acid dissociation type, that is, AH···B ⇔ A(-)···HB(+)(but without complete proton transfer), in both polar and nonpolar solvents, with special attention given to the variation of νAH with the solvent's dielectric constant ε. The theory involves a valence bond (VB) model for the complex's electronic structure, quantization of the complex's proton and H-bond motions, and a solvent coordinate accounting for nonequilibrium solvation. A general prediction is that νAH decreases with increasing ε largely due to increased solvent stabilization of the ionic VB structure A(-)···HB(+) relative to the neutral VB structure AH···B. Theoretical νAH versus 1/ε slope expressions are derived; these differ for polar and nonpolar solvents and allow analysis of the solvent dependence of νAH. The theory predicts that both polar and nonpolar slopes are determined by (i) a structure factor reflecting the complex's size/geometry, (ii) the complex's dipole moment in the ground vibrational state, and (iii) the dipole moment change in the transition, which especially reflects charge transfer and the solution phase proton potential shapes. The experimental proton frequency solvent dependence for several OH···O H-bonded complexes is successfully accounted for and analyzed with the theory.

Robust Diffusive Proton Motions in Phase IV of Solid Hydrogen

Systematic first-principles molecular dynamics (MD) simulations with long simulation times (7–13 ps) for phase IV of solid hydrogen using different supercell sizes of 96, 288, 576, and 768 atoms established that the diffusive proton motions process in the graphene-like layer is an intrinsic property and independent of the simulation cell sizes. The present study highlights an often overlook issue in first-principles calculations that long time MD is essential to achieve ergodicity, which is mandatory for a proper description of dynamics of a system. It is inappropriate to make arguments on the analysis of MD results, which are far from ergodic. Furthermore, we have simulated the vibrational density of states of phase IV based on our proton diffuse model at a pressure range of 225–300 GPa, which is qualitatively in agreement with experimental data.

Deformation properties of the projected spherical single particle basis

Deformed single particle energies obtained by averaging a particle–core Hamiltonian with a projected spherical basis depend on a deformation parameter and an arbitrary constant defining the canonical transformation relating the collective quadrupole coordinates and momenta with the boson operators. When the mentioned basis describes the single particle motion of either protons or neutrons the parameters involved are isospin dependent. An algorithm for fixing these parameters is formulated and then applied for 194 isotopes covering a good part of the nuclide chart. Relation with the Nilsson deformed basis is pointed out in terms of deformation dependence of the corresponding single particle energies as well as of the nucleon densities and their symmetries. The proposed projected spherical basis provides an efficient tool for the description of spherical and deformed nuclei in a unified fashion.

Mixed quantum classical calculation of proton transfer reaction rates: from deep tunneling to over the barrier regimes.

We present mixed quantum classical calculations of the proton transfer (PT) reaction rates represented by a double well system coupled to a dissipative bath. The rate constants are calculated within the so called nontraditional view of the PT reaction, where the proton motion is quantized and the solvent polarization is used as the reaction coordinate. Quantization of the proton degree of freedom results in a problem of non-adiabatic dynamics. By employing the reactive flux formulation of the rate constant, the initial sampling starts from the transition state defined using the collective reaction coordinate. Dynamics of the collective reaction coordinate is treated classically as over damped diffusive motion, for which the equation of motion can be derived using the path integral, or the mixed quantum classical Liouville equation methods. The calculated mixed quantum classical rate constants agree well with the results from the numerically exact hierarchical equation of motion approach for a broad range of model parameters. Moreover, we are able to obtain contributions from each vibrational state to the total reaction rate, which helps to understand the reaction mechanism from the deep tunneling to over the barrier regimes. The numerical results are also compared with those from existing approximate theories based on calculations of the non-adiabatic transmission coefficients. It is found that the two-surface Landau-Zener formula works well in calculating the transmission coefficients in the deep tunneling regime, where the crossing point between the two lowest vibrational states dominates the total reaction rate. When multiple vibrational levels are involved, including additional crossing points on the free energy surfaces is important to obtain the correct reaction rate using the Landau-Zener formula.

The role of large-amplitude motions in the spectroscopy and dynamics of ${\rm H}_5^+$H5+

Protonated hydrogen dimer, H₅⁺, is the intermediate in the astrochemically important proton transfer reaction between H₃⁺ and H2. To understand the mechanism for this process, we focus on how large amplitude motions in H₅⁺ result in scrambling of the five hydrogen atoms in the collision complex. To this end, the one-dimensional zero-point corrected potential surfaces were mapped out as functions of reaction coordinates for the H₃⁺ + H2 collision using minimized energy path diffusion Monte Carlo [C. E. Hinkle and A. B. McCoy, J. Phys. Chem. Lett. 1, 562 (2010)]. In this study, the previously developed approach was extended to allow for the investigation of selected excited states that are expected to be involved in the proton scrambling dynamics. Specifically, excited states in the shared proton motion between the two H2 groups, and in the outer H2 bending motions were investigated. Of particular interest is the minimum distance between H₃⁺ and H2 at which all five hydrogen atoms become free to exchange. In addition, this diffusion Monte Carlo-based approach was used to determine the zero-point energy E0, the dissociation energy D0, and excitation energies associated with the vibrational motions that were investigated. The evolution of the wave functions was also studied, with a focus on how the intramolecular vibrations in H₅⁺ evolve into motions of H₃⁺ or H2. In the case of the proton scrambling, we find that the relevant transition states become fully accessible at separations between H₃⁺ and H2 of approximately 2.15 Å, a distance that is accessed by the excited states of H₅⁺ with two or more quanta in the shared proton stretch. The implications of this finding on the vibrational spectroscopy of H₅⁺ are also discussed.

Proton conduction in nanopores of sol–gel-derived porous glasses and thin films

Nanoporous glasses and nanoporous thin films were prepared using sol–gel method, and proton conductivities in nanopores of sol–gel-derived porous glasses and thin films are overviewed in this paper. Proton motions inside nanopores were monitored by impedance and nuclear magnetic resonance (NMR) spectroscopies. The impedance data is correlated with the proton motion in bulk scale, whereas NMR data is correlated with that in nanometer scale, respectively. From the comparison of the activation energies obtained from impedance and NMR spectroscopies, percolation of proton conducting path and its relation to the amount of absorbed water molecules are shown. In the case of nanoporous thin films, directions of pores can be controlled by using cationic and non-ionic surfactants. Relationship between direction of pores and proton conductivity is discussed based on impedance test results.

TEST-PARTICLE ACCELERATION IN A HIERARCHICAL THREE-DIMENSIONAL TURBULENCE MODEL

The acceleration of charged particles is relevant to the solar corona over a broad range of scales and energies. High-energy particles are usually detected in concomitance with large energy release events like solar eruptions and flares, nevertheless acceleration can occur at smaller scales, characterized by dynamical activity near current sheets. To gain insight into the complex scenario of coronal charged particle acceleration, we investigate the properties of acceleration with a test-particle approach using three-dimensional magnetohydrodynamic (MHD) models. These are obtained from direct solutions of the reduced MHD equations, well suited for a plasma embedded in a strong axial magnetic field, relevant to the inner heliosphere. A multi-box, multi-scale technique is used to solve the equations of motion for protons. This method allows us to resolve an extended range of scales present in the system, namely from the ion inertial scale of the order of a meter up to macroscopic scales of the order of $10\,$km ($1/100$th of the outer scale of the system). This new technique is useful to identify the mechanisms that, acting at different scales, are responsible for acceleration to high energies of a small fraction of the particles in the coronal plasma. We report results that describe acceleration at different stages over a broad range of time, length and energy scales.

Pattern recognition and data mining software based on artificial neural networks applied to proton transfer in aqueous environments

In computational physics proton transfer phenomena could be viewed as pattern classification problems based on a set of input features allowing classification of the proton motion into two categories: transfer ‘occurred’ and transfer ‘not occurred’. The goal of this paper is to evaluate the use of artificial neural networks in the classification of proton transfer events, based on the feed-forward back propagation neural network, used as a classifier to distinguish between the two transfer cases. In this paper, we use a new developed data mining and pattern recognition tool for automating, controlling, and drawing charts of the output data of an Empirical Valence Bond existing code. The study analyzes the need for pattern recognition in aqueous proton transfer processes and how the learning approach in error back propagation (multilayer perceptron algorithms) could be satisfactorily employed in the present case. We present a tool for pattern recognition and validate the code including a real physical case study. The results of applying the artificial neural networks methodology to crowd patterns based upon selected physical properties (e.g., temperature, density) show the abilities of the network to learn proton transfer patterns corresponding to properties of the aqueous environments, which is in turn proved to be fully compatible with previous proton transfer studies.

Electron-nuclear dynamics of the one-electron nonlinear polyatomic molecule H32+in ultrashort intense laser pulses

A quantum description of the one-electron triangular H${}_{3}^{2+}$ molecular ion, beyond the Born-Oppenheimer approximation, is used to study the full influence of the nuclear motion on the high-intensity photoionization and harmonic generation processes. A detailed analysis of electron and proton motions and their time-dependent acceleration allows for identification of the main electron recollision events as a function of time-dependent configuration of the protons. High-order-harmonic generation photons are shown to be produced by single-electron recollision in the second half of the pulse envelope, which also induces a redshift in the harmonics, due to the rapid few-femtosecond motions of protons. Perpendicular harmonics are produced, in general, with a linearly polarized laser pulse parallel to a bond of the triangular molecule, and, in particular, the harmonics in the cutoff region are elliptically polarized. When the laser-pulse polarization is parallel to a symmetry axis of the triangular molecular ion, creation and destruction of the chemical bond perpendicular to the polarization is predicted on a near-femtosecond time scale.

Fragmentation of Hydrocarbon Molecules in Intense Laser Fields Studied by Coincidence Momentum Imaging: A Review

Fragmentation of polyatomic molecules is a fundamental chemical reaction in intense laser fields when the electric field strength of the laser pulse is comparable to or exceeds the intra-molecular Coulomb binding fields. For hydrocarbon molecules, because of the migration of light hydrogen atom (or proton) that can lead to chemical bond rearrangement of molecules, fragmentation of hydrocarbon molecules may result in new fragment species that could not be realized from the initial geometry of molecules by direct bond breaking, making the full characterization of their dynamical fragmentation processes difficult. In this article, we will review recent progress in the study of fragmentation of hydrocarbon molecules induced by intense laser fields using the coincidence momentum imaging method that can provide definite information on the fragmentation channels of molecules. The effect of hydrogen migration on fragmentation of hydrocarbon molecules is reviewed, based on which new possible schemes for controlling chemical bond breaking/formation by controlling the motion of protons within a hydrocarbon molecule is discussed.

A highly conductive proton exchange membrane for high temperature fuel cells based on poly(5-vinyl tetrazole) and sulfonated polystyrene

Poly(5-vinyl tetrazole) (PVTra) with 85% molar content of tetrazole was prepared by [3 + 2] cyclo-addition of polyacrylonitrile (PAN) with sodium azide. The membranes of PVTra(SPS) x were prepared by blending different ratios of PVTra to sulfonated polystyrene (SPS) (SD = 72%). The on-set degradation temperature of the PVTra(SPS) x is above 180 °C. The degradation behaviors related with the acid–base interaction were analyzed. The membranes were confirmed to retain 0–5% water vapor at 80–140 °C in air due to the hydrophily of highly sulfonated polystyrene. The membrane PVTra(SPS) 2 shows the proton conductivity of 10 − 2 S/cm at 100 °C and even around 4 × 10 − 2 S/cm at 120 °C without extra humidity supply and is very promising for high temperature fuel cells with low humidity. The high proton conductivity is ascribed to the unique composition in which the heterocyclic polymer provides the proton motion by construction diffusion and the highly sulfonated polymer retains water vapor to lower the activation energy for proton conduction. The possible proton conduction sketch map is provided. • The novel PVTra(SPS)x membranes were prepared. • The PVTra(SPS)x shows high proton conductivity at high temperature with low humidity. • The PVTra(SPS)x are flexible and don’t show fragility as the pristine SPS. • The PVTra(SPS)x retains water vapor facilitating proton conduction. • A sketch map summarizes the functions of the membrane components in proton conduction.

Anhydrous proton motion study by solid state NMR spectroscopy in novel PEMFC blend membranes composed of fluorinated copolymer bearing 1,2,4-triazole functional groups and sPEEK

The proton mobility in a new family of PEMFC blend membranes containing 1,2,4-triazole groups is studied by infrared and solid state NMR spectroscopies.

Isotopic differentiation and sublattice melting in dense dynamic ice

The isotopes of hydrogen provide a unique exploratory laboratory for examining the role of zero point energy (ZPE) in determining the structural and dynamic features of the crystalline ices of water. There are two critical regions of high pressure: (i) near 1 TPa and (ii) near the predicted onset of metallization at around 5 TPa. At the lower pressure of the two, we see the expected small isotopic effects on phase transitions. Near metallization, however, the effects are much greater, leading to a situation where tritiated ice could skip almost entirely a phase available to the other isotopomers. For the higher pressure ices, we investigate in some detail the enthalpics of a dynamic proton sublattice, with the corresponding structures being quite ionic. The resistance toward diffusion of single protons in the ground state structures of high-pressure H2O is found to be large, in fact to the point that the ZPE reservoir cannot overcome these. However, the barriers toward a three-dimensional coherent or concerted motion of protons can be much lower, and the ensuing consequences are explored.

Pyridine N-oxide/trichloroacetic acid complex in acetonitrile: FTIR spectra, anharmonic calculations and computations of 1–3D potential surfaces of O–H vibrations

FTIR spectra of pyridine N-oxide and trichloroacetic acid H-bonded complex in acetonitrile were studied at 20 and 50°C. The calculations of equilibrium configurations of the complex and their IR spectra in harmonic- and anharmonic approximations were carried out at the level of B3LYP/cc-pVTZ/PCM. However both approximations turned out to be incompetent determining the frequency of the O–Н stretching vibration. In order to reveal the causes of essential discrepancies between calculated and experimental data one-, two- and three-dimensional potential energy surfaces (PES) of the O–H…O bridge proton motion in the frame of fixed other atoms in the complex were calculated. The frequencies of O–H…O stretching and bending vibrations were calculated by numerical solution of the Schrödinger equation. It is shown that only the approach of proton motion on the 3D PES allows obtaining a good agreement between the calculated and the experimental values of the frequencies of the О–Н stretching vibrations.