NH4+ Deprotonation at Interfaces Induced Reversible H3O+/NH4+ Co-insertion/Extraction

Ion insertions always involve electrode-electrolyte interface process, desolvation for instance, which determines the electrochemical kinetics. However, it′s still a challenge to achieve fast ion insertion and investigate ion transformation at interface. Herein, the interface deprotonation of NH₄⁺ and the introduced dissociation of H₂O molecules to provide sufficient H₃O⁺ to insert into materials′ structure for fast energy storages are revealed. Lewis acidic ion-NH₄⁺ can, on one hand provide H₃O⁺ itself via deprotonation, and on the other hand hydrolyze with H₂O molecules to produce H₃O⁺. In situ attenuated total reflection-Fourier transform infrared ray method probed the interface accumulation and deprotonation of NH₄⁺, and density functional theory calculations manifested that NH₄⁺ tend to thermodynamically adsorb on the surface of monoclinic VO₂, and deprotonate to provide H₃O⁺. In addition, the inserted NH₄⁺ has a positive effect for stabilizing the VO₂(B) structure. Therefore, high specific capacity (>300 mAh g⁻¹) and fast ionic insertion/extraction (<20 s) can be realized in VO₂(B) anode. This interface derivation proposes a new path for designing proton ion insertion/extraction in mild electrolyte.     

Synthesis and characterization of three novel cation-containing (NH4+/C3H7NH3+/NH3+C2H4NH3+) aluminum diphosphonates

Three new aluminum diphosphonates (C(3)H(7)NH(3))[AlF[(HO)O(2)PC(2)H(4)PO(3)]] (1) (orthorhombic, Pnma, a = 8.2048(1) A, b = 6.90056(6) A, c = 19.6598(4) A, Z = 4), (H(3)NC(2)H(4)NH(3))[Al(OH)(O(3)PC(2)H(4)PO(3))] (2) (monoclinic, P2(1)/n, a = 11.142(3) A, b = 7.008(2) A, c = 12.903(5) A, beta = 96.24(7) degrees, Z = 4), and (NH(4))(2)[AlF(O(3)PCH(2)PO(3))] (3) (orthorhombic, Cmcm, a = 16.592(2) A, b = 7.5106(9) A, c = 7.0021(9) A, Z = 4) have been synthesized by solvothermal methods in the presence of linear organic ammonium cations (for 1 and 2) and ammonium cations (for 3) and their structures determined using powder, microcrystal, and single-crystal X-ray diffraction data, respectively. All three materials contain a similar one-dimensional chain motif which is related to that found in the mineral Tancoite. This chain motif consists of corner-sharing octahedra (AlO(4)F(2) for 1 and 3 and AlO(6) for 2) linked together through the bridging CPO(3) tetrahedra of the diphosphonate groups. These chains are unusual in that each diphosphonate moiety acts as a bisbidentate ligand that is coordinated to the same two metal centers through both of the O(3)PC- groups of the diphosphonate ligand. The arrangement of the Tancoite-like chains and charge compensation cations in the structures of compounds 1-3 is seen to be dependent upon the nature of the diphosphonic acid and organoammonium/ammonium cations. Careful selection of these two components may provide a method to design future materials in this system.     

Thermochemistry and accurate quantum reaction rate calculations for H2/HD/D2 + CH3

Accurate quantum-mechanical results for thermodynamic data, cumulative reaction probabilities (for J = 0), thermal rate constants, and kinetic isotope effects for the three isotopic reactions H2 + CH3 --> CH4 + H, HD + CH3 --> CH4 + D, and D2 + CH3 --> CH(3)D + D are presented. The calculations are performed using flux correlation functions and the multiconfigurational time-dependent Hartree (MCTDH) method to propagate wave packets employing a Shephard interpolated potential energy surface based on high-level ab initio calculations. The calculated exothermicity for the H2 + CH3 --> CH4 + H reaction agrees to within 0.2 kcal/mol with experimentally deduced values. For the H2 + CH3 --> CH4 + H and D2 + CH3 --> CH(3)D + D reactions, experimental rate constants from several groups are available. In comparing to these, we typically find agreement to within a factor of 2 or better. The kinetic isotope effect for the rate of the H2 + CH3 --> CH4 + H reaction compared to those for the HD + CH3 --> CH4 + D and D2 + CH3 --> CH(3)D + D reactions agree with experimental results to within 25% for all data points. Transition state theory is found to predict the kinetic isotope effect accurately when the mass of the transferred atom is unchanged. On the other hand, if the mass of the transferred atom differs between the isotopic reactions, transition state theory fails in the low-temperature regime (T < 400 K), due to the neglect of the tunneling effect.     

Quantum dynamics study of H+NH3-->H2+NH2 reaction

We report in this paper a quantum dynamics study for the reaction H+NH3-->NH2+H2 on the potential energy surface of Corchado and Espinosa-Garcia [J. Chem. Phys. 106, 4013 (1997)]. The quantum dynamics calculation employs the semirigid vibrating rotor target model [J. Z. H. Zhang, J. Chem. Phys. 111, 3929 (1999)] and time-dependent wave packet method to propagate the wave function. Initial state-specific reaction probabilities are obtained, and an energy correction scheme is employed to account for zero point energy changes for the neglected degrees of freedom in the dynamics treatment. Tunneling effect is observed in the energy dependency of reaction probability, similar to those found in H+CH4 reaction. The influence of rovibrational excitation on reaction probability and stereodynamical effect are investigated. Reaction rate constants from the initial ground state are calculated and are compared to those from the transition state theory and experimental measurement.     

DWBA predicted relative product rotational state distribution for H + D2 → HD + D

Relative product rotational state distributions for H + D₂ → HD + D are reported based on the DWBA of Suck Salk, and are shown to agree reasonably well with observations. The rotational peak positions are found to have good correlation with computed “semiclassical” angular momentum.     

Renner-Teller quantum dynamics of the N(2D) + H2-->NH + H reaction

We present the Born-Oppenheimer (BO) and Renner-Teller (RT) quantum dynamics of the reaction (14)N((2)D)+(1)H(2)(X (1)Sigma(g) (+))-->NH(X (3)Sigma(-))+H((2)S), considering the NH(2) electronic states X (2)B(1) and A (2)A(1). These states correlate to the same (2)Pi(u) linear species, are coupled by RT nonadiabatic effects, and give NH(X (3)Sigma(-))+H and NH(a (1)Delta)+H, respectively. We develop the Hamiltonian matrix elements in the R embedding of the Jacobi coordinates and in the adiabatic electronic representation, using the permutation-inversion symmetry, and taking into account the nuclear-spin statistics. Collision observables are calculated via the real wave-packet (WP) and flux methods, using the potential-energy surfaces of Santoro et al. [J. Phys. Chem. A 106, 8276 (2002)]. WP snapshots show that the reaction proceeds via an insertion mechanism, and that the RT-WP avoids the A (2)A(1) potential barrier, jumping from the excited to the ground surface and giving mainly the NH(X (3)Sigma(-)) products. X (2)B(1) BO probabilities and cross sections show large tunnel effects and are approximately four to ten times larger than the A (2)A(1) ones. This implies a BO rate-constant ratio k(X (2)B(1))k(A (2)A(1)) approximately 10(5) at 300 K, i.e., a negligible BO formation of NH(a (1)Delta). When H(2) is rotationally excited, RT couplings reduce slightly the X (2)B(1) reaction observables, but enhance strongly the A (2)A(1) reactivity. These couplings are important at all collision energies, reduce the collision threshold, and increase remarkably reaction probabilities and cross sections. The RT k(A (2)A(1)) is thus approximately 3.3 order of magnitude larger than the BO value, and degeneracy-averaged, initial-state-resolved rate constants increase by approximately 13% and by approximately 47% at 300 and 500 K, respectively. Owing to an overestimation of the X (2)B(1) potential barrier, the calculated thermal rate is too low with respect to that observed, but we obtain a good agreement by shifting down the calculated cross section.     

Ab initio thermal rate coefficients for H + NH3 ⇌ H2 + NH2

The reversible reaction NH₃ + H ⇌ H₂ + NH₂, which plays an important role in NH₃ fuel combustion, is studied with a theoretical approach that combines the high-accuracy extrapolated ab initio thermochemistry (HEAT) protocol with semiclassical transition state theory (SCTST). The calculated forward reaction is endothermic by 11.8 ± 1 kJ/mol, in nearly perfect agreement with the active thermochemical tables (ATcT) value of 11.5 ± 0.2 kJ/mol. Using this improved thermochemistry yields better rate constants, especially at low temperatures. Experimental rate constants available from 400 to 2000 K for the forward and reverse reaction pathways can be reproduced (within 20%) by the calculations from first principles.     

The state-to-state-to-state model for direct chemical reactions: application to D+H2-->HD+H

A simple theoretical model is developed to predict the state-to-state dynamics of direct chemical reactions. Motivated by traditional ideas from transition state theory, expressions are derived for the reactive S matrix that may be computed using the local transition state dynamics. The key approximation involves the use of quantum bottleneck states to represent the near separable dynamics taking place near the transition state. Explicit expressions for the S matrix are obtained using a Franck-Condon treatment for the inelastic coupling between internal states of the collision complex. It is demonstrated that the energetic thresholds for various initial reagent states of the D+H(2) reaction can be understood in terms of our theory. Specifically, the helicity of the reagent states are found to correlate directly to the symmetry of the quantum bottleneck states, which thus possess very different thresholds. Furthermore, the rotational product state distributions for D+H(2) are found to be associated with interfering pathways through the quantum bottleneck states.     

Kinetics and product branching ratios of the reaction of (1)CH2 with H2 and D2

The reactions of singlet methylene (a(1)A1 (1)CH2) with hydrogen and deuterium have been studied by experimental and theoretical techniques. The rate coefficients for the removal of singlet methylene with H2 (k1) and D2 (k2) have been measured from 195 to 798 K and are essentially temperature-independent with values of k1 = (10.48 +/- 0.32) x 10(-11) cm(3) molecule(-1) s(-1) and k2 = (5.98 +/- 0.34) x 10(-11) cm(3) molecule(-1) s(-1), where the errors represent 2sigma, giving a ratio of k1/k2 = 1.75 +/- 0.11. In the reaction with H2, singlet methylene can be removed by reaction giving CH3 + H or deactivated to ground-state triplet methylene. Direct measurement of the H atom product showed that the fraction of relaxation decreased from 0.3 at 195 K to essentially zero at 398 K. For the reaction with deuterium, either H or D may be eliminated. Experimentally, the H:D ratio was determined to be 1.8 +/- 0.5 over the range 195-398 K. Theoretically, the reaction kinetics has been predicted with variable reaction coordinate transition state theory and with rigid-body trajectory simulations employing various high-level, ab initio-determined potential energy surfaces. The magnitudes of the calculated rate coefficients are in agreement with experiment, but the calculations show a significant negative temperature dependence that is not observed in the experimental results. The calculated and experimental H to D ratios from the reaction of singlet methylene with D2 are in good agreement, suggesting that the reaction proceeds entirely through the formation of a long-lived methane intermediate with a statistical distribution of energy.     

Seven-dimensional quantum dynamics study of the H+NH3-->H2+NH2 reaction

Initial state-selected time-dependent wave packet dynamics calculations have been performed for the H+NH3-->H2+NH2 reaction using a seven-dimensional model and an analytical potential energy surface based on the one developed by Corchado and Espinosa-Garcia [J. Chem. Phys. 106, 4013 (1997)]. The model assumes that the two spectator NH bonds are fixed at their equilibrium values. The total reaction probabilities are calculated for the initial ground and seven excited states of NH3 with total angular momentum J=0. The converged cross sections for the reaction are also reported for these initial states. Thermal rate constants are calculated for the temperature range 200-2000 K and compared with transition state theory results and the available experimental data. The study shows that (a) the total reaction probabilities are overall very small, (b) the symmetric and asymmetric NH stretch excitations enhance the reaction significantly and almost all of the excited energy deposited was used to reduce the reaction threshold, (c) the excitation of the umbrella and bending motion have a smaller contribution to the enhancement of reactivity, (d) the main contribution to the thermal rate constants is thought to come from the ground state at low temperatures and from the stretch excited states at high temperatures, and (e) the calculated thermal rate constants are three to ten times smaller than the experimental data and transition state theory results.     

Chemi-luminescence measurements of hyperthermal Xe+/Xe2+ + NH3 reactions

Luminescence spectra are recorded for the reactions of Xe(+) + NH(3) and Xe(2+) + NH(3) at energies ranging from 11.5 to 206 eV in the center-of-mass (E(cm)) frame. Intense features of the luminescence spectra are attributed to the NH (A (3)Π(i)-X (3)Σ(-)), hydrogen Balmer series, and Xe I emission observable for both primary ions. Evidence for charge transfer products is only found through Xe I emission for both primary ions and NH(+) emission for Xe(2+) primary ions. For both primary ions, the absolute NH (A-X) cross section increases with collision energy before leveling off at a constant value, approximately 9 × 10(-18) cm(2), at about 50 eV while H-α emission increases linearly with collision energy. The nascent NH (A) populations derived from the spectral analysis are found to be independent of collision energy and have a constant rotational temperature of 4200 K.     

Ab initio study of the ClO + NH2 reaction: prediction of the total rate constant and product branching ratios

The mechanism for ClO + NH2 has been investigated by ab initio molecular orbital and transition-state theory calculations. The species involved have been optimized at the B3LYP/6-311+G(3df,2p) level and their energies have been refined by single-point calculations with the modified Gaussian-2 method, G2M(CC2). Ten stable isomers have been located and a detailed potential energy diagram is provided. The rate constants and branching ratios for the low-lying energy channel products including HCl + HNO, Cl + NH2O, and HOCl + 3NH (X(3)Sigma(-)) are calculated. The result shows that formation of HCl + HNO is dominant below 1000 K; over 1000 K, Cl + NH2O products become dominant. However, the formation of HOCl + 3NH (X(3)Sigma(-)) is unimportant below 1500 K. The pressure-independent individual and total rate constants can be expressed as k1(HCl + HNO) = 4.7 x 10(-8)(T(-1.08)) exp(-129/T), k(2)(Cl + NH2O) = 1.7 x 10(-9)(T(-0.62)) exp(-24/T), k3(HOCl + NH) = 4.8 x 10(-29)(T5.11) exp(-1035/T), and k(total) = 5.0 x 10(-9)(T(-0.67)) exp(-1.2/T), respectively, with units of cm(3) molecule(-1) s(-1), in the temperature range of 200-2500 K.     

Experimental and theoretical investigations of the reactions NH(X 3Sigma-) + D(2S)-->ND(X 3Sigma-) + H(2S) and NH(X 3Sigma-) + D(2S)-->N(4S) + HD(X 1Sigmag+)

The rate coefficient of the reaction NH(X (3)Sigma(-))+D((2)S)-->(k(1) )products (1) is determined in a quasistatic laser-flash photolysis, laser-induced fluorescence system at low pressures. The NH(X) radicals are produced by quenching of NH(a (1)Delta) (obtained in the photolysis of HN(3)) with Xe and the D atoms are generated in a D(2)/He microwave discharge. The NH(X) concentration profile is measured in the presence of a large excess of D atoms. The room-temperature rate coefficient is determined to be k(1)=(3.9+/-1.5) x 10(13) cm(3) mol(-1) s(-1). The rate coefficient k(1) is the sum of the two rate coefficients, k(1a) and k(1b), which correspond to the reactions NH(X (3)Sigma(-))+D((2)S)-->(k(1a) )ND(X (3)Sigma(-))+H((2)S) (1a) and NH(X (3)Sigma(-))+D((2)S)-->(k(1b) )N((4)S)+HD(X (1)Sigma(g) (+)) (1b), respectively. The first reaction proceeds via the (2)A(") ground state of NH(2) whereas the second one proceeds in the (4)A(") state. A global potential energy surface is constructed for the (2)A(") state using the internally contracted multireference configuration interaction method and the augmented correlation consistent polarized valence quadrupte zeta atomic basis. This potential energy surface is used in classical trajectory calculations to determine k(1a). Similar trajectory calculations are performed for reaction (1b) employing a previously calculated potential for the (4)A(") state. The calculated room-temperature rate coefficient is k(1)=4.1 x 10(13) cm(3) mol(-1) s(-1) with k(1a)=4.0 x 10(13) cm(3) mol(-1) s(-1) and k(1b)=9.1 x 10(11) cm(3) mol(-1) s(-1). The theoretically determined k(1) shows a very weak positive temperature dependence in the range 250< or =TK< or =1000. Despite the deep potential well, the exchange reaction on the (2)A(") ground-state potential energy surface is not statistical.     

Seven dimensional quantum dynamics study of the H2+NH2-->H+NH3 reaction

Initial state-selected time-dependent wave packet dynamics calculations have been performed for the H2+NH2-->H+NH3 reaction using a seven dimensional model on an analytical potential energy surface based on the one developed by Corchado and Espinosa-Garcia [J. Chem. Phys. 106, 4013 (1997)]. The model assumes that the two spectator NH bonds are fixed at their equilibrium values and nonreactive NH2 group keeps C2v symmetry and the rotation-vibration coupling in NH2 is neglected. The total reaction probabilities are calculated when the two reactants are initially at their ground states, when the NH2 bending mode is excited, and when H2 is on its first vibrational excited state, with total angular momentum J=0. The converged cross sections for the reaction are also reported for these initial states. Thermal rate constants and equilibrium constants are calculated for the temperature range of 200-2000 K and compared with transition state theory results and the available experimental data. The study shows that (a) the reaction is dominated by ground-state reactivity and the main contribution to the thermal rate constants is thought to come from this state, (b) the excitation energy of H2 was used to enhance reactivity while the excitation of the NH2 bending mode hampers the reaction, (c) the calculated thermal rate constants are very close to the experimental data and transition state theory results at high and middle temperature, while they are ten times higher than that of transition state theory at low temperature (T=200 K), and (d) the equilibrium constants results indicate that the approximations applied may have different roles in the forward and reverse reactions.     

Molecular beam scattering studies of the reaction D + H2 (v = 0) and D + H2 (v = 1) → HD + H

The reaction D + H₂ → HD + H has been investigated in two molecular beam scattering experiments. Angular and time-of-flight distributions have been measured for the initial vibrational ground state (v = 0) at a most probable collision energy of E_cm = 1.5 eV and for the first vibrational excited state (v = 1) at E_cm = 0.28 eV with the same apparatus. Results for the ground-state experiment are compared with quasiclassical trajectory calculations(QCT) on the LSTH-hypersurface transformed into the laboratory system and averaged over the apparatus distributions. The agreement isquite satisfactory. At this high collision energy the HD products are no longer scattered in a backward direction but in a wide angular region concentrated about θ = 90° in the center-of-mass system. The absolute reactive cross section has been determined and the agreement with the theoretical value from QCT calculations is within the experimental error. The high sensitivity of the experiment to different properties of the doubly differential cross section has also been demonstrated. A preliminary evaluation of the experiment with initial vibrational excitation (v = 1) shows that the HD-product molecules are preferably backward scattered and the change of internal energy is small supporting the concept of a reaction which is adiabatic with respect to the internal degrees of freedom.     

Reaction rates for O + HD → OH + D and O + HD → OD + H

We have calculated reaction rates for the reactions O + HD → OH + D and O + DH → OD + H using improved canonical variational transition state theory and least-action ground-state transmission coefficients with an ab initio potential energy surface. The kinetic isotope effects are in good agreement with experiment. The optimized tunneling paths and properties of the variational transition states and the rate enhancement for vibrationally excited reactants are also presented and compared with those for the isotopically unsubstituted reaction O + H₂ → OH + H. The thermal reactions at low and room temperature are predicted to occur by tunneling at extended configurations, i.e., to initiate early on the reaction path and to avoid the saddle point regions. Tunneling also dominates the low and room temperature reactions for excited vibrational states, but in these cases the results are not as sensitive to the nature of the tunneling path. Overbarrier mechanisms dominate for both thermal and excited-vibrational state reactions for T > 600 K. For the excited-state reaction (with initial vibrational quantum number n > 0) a transition state switch occurs for T > 1000 K for the O + HD(n = 1) → OD + H case and for T > 1500 K for the O + DH(n = 1) → OD + H reaction, and this may be a general phenomenon for excited-state reactions at higher temperature. In the present case the switch occurs from an early variational transition state where the vibrationally adiabatic approximation is expected to be valid to a tighter variational transition state where nonadiabatic effects are probably important and should be included.     

Primary branching ratios for the low-temperature reaction of state-prepared N2+ with CH4, C2H2, and C2H4

Product branching ratios (BRs) are reported for ion-molecule reactions of state-prepared nitrogen cation (N(2)(+)) with methane (CH(4)), acetylene (C(2)H(2)). and ethylene (C(2)H(4)) at low temperature using a modified ion imaging apparatus. These reactions are performed in a supersonic nozzle expansion characterized by a rotational temperature of 40 ± 5K. For the N(2)(+) + CH(4) reaction, a BR of 0.83:0.17 is obtained for the dissociative charge-transfer (CT) reaction that gives rise to the formation of CH(3)(+) and CH(2)(+) product ions, respectively. The N(2)(+) + C(2)H(2) ion-molecule reaction proceeds through a nondissociative CT process that results in the sole formation of C(2)H(2)(+) product ions. The reaction of N(2)(+) with C(2)H(4) leads to the formation of C(2)H(3)(+) and C(2)H(2)(+) product ions with a BR of 0.74:0.26, respectively. The reported BR for the N(2)(+) + C(2)H(4) reaction is supportive of a nonresonant dissociative CT mechanism similar to the one that accompanies the N(2)(+) + CH(4) reaction. No dependence of the branching ratios on N(2)(+) rotational level was observed. In addition to providing direct insight into the dynamics of the state-prepared N(2)(+) ion-molecule reactions with the target neutral hydrocarbon molecules, the reported low-temperature BRs are also important for accurate modeling of the nitrogen-dominated upper atmosphere of Saturn's moon, Titan.     

Full dimensional time-dependent quantum dynamics study of the H + NH3 --> H2 + NH2 reaction

A rigorous full dimensional time-dependent wave packet method has been developed for the reactive scattering between an atom and a tetra-atomic molecule. The method has been applied to the hydrogen abstraction reaction H+NH(3)-->H(2)+NH(2). Initial state-selected total reaction probabilities are investigated for the reactions from the ground vibrational state and from four excited vibrational states of ammonia. The total reaction probabilities from two lowest "tunneling doublets" due to the inversion barrier for the umbrella bending motion of NH(3) and from two pairs of doubly degenerate vibrational states of NH(3) are also inspected. Integral cross sections and rate constants are calculated for the reaction from the ground state with the centrifugal-sudden approximation. The calculated results are compared with those from the previous seven dimensional calculations [M. Yang and J. C. Corchado, J. Chem. Phys. 126, 214312 (2007)]. This work shows that the full dimensional rate constants are a factor of 3 larger than the corresponding seven dimensional calculated values at T=200 K and are overall smaller than those obtained from the variational transition state theory in the whole temperature region. The work also reveals that nonreactive NH bonds of NH(3) cannot be treated as spectators due to the fact that three NH bonds are coupled with each other during the reaction process.     

A study of the nearly thermoneutral reactions of N+ with H2, HD and D2

The rate coefficients k for the nearly thermoneutral atom abstraction reactions of N⁺ ions with H₂, HD and D₂ have been determined as a function of ion-molecule centre-of-mass energy, KE_cm, in a SIFDT apparatus, over the range of KE_cm from thermal energy at 300 K to ≈ 0.5 eV. From Arrhenius-type plots of ln k versus (KE_cm)⁻¹, values of the thermicities of the reactions, ΔE, have been determined. The differences in the values of ΔE obtained for the reactions are accounted for by differences in the vibrational zero-point energies of the reactant and product molecules. From the data, the absolute proton affinity of the N atom is found to be 3.531 eV.