Probing the Relationship Between Large-Amplitude Motions in H₅⁺ and Proton Exchange Between H₃⁺ and H₂

Understanding the spectroscopy and dynamics of H₅⁺ is central in gaining insights into the H₃⁺ + H₂ → H₅⁺ → H₂ + H₃⁺ proton transfer reaction. This molecular ion exhibits large-amplitude vibrations, which allow for the transfer of a proton between H₃⁺ and H₂ even in its ground vibrational state. With vibrational excitation, the number of open channels for permutations of protons increase. In this work, the minimized energy path variant of diffusion Monte Carlo is used to investigate how the energetically accessible proton permutations evolve as H₅⁺ is dissociated into H₃⁺ + H₂. Two mechanisms for proton permutation are investigated. The first is the proton hop, which correlates to large-amplitude vibrations of the central proton in H₅⁺. The second is the exchange of a pair of hydrogen atoms between H₃⁺ and H₂. This mechanism requires several proton hops along with a 120° rotation of H₃⁺ within the H₅⁺ molecular ion. This analysis shows that while there is a narrow region of configuration space over which both isomerization processes are energetically accessible, full permutation of the five protons in H₅⁺ more likely occurs through a stepwise mechanism. Such full permutation of the protons becomes accessible when the shared proton stretch is excited to the <i>v</i>_pt = 2 or 3 excited state. The effects of deuteration and rotational excitation of the H₂ and H₃⁺ products are also investigated. Deuteration inhibits permutation of protons, while rotational excitation has only a small impact on these processes

Investigation of the Structure and Spectroscopy of H₅⁺ Using Diffusion Monte Carlo

The results of diffusion Monte Carlo (DMC) calculations of the ground and selected excited states of H₅⁺ and its deuterated analogues are presented. Comparisons are made between the results obtained from two recently reported potential surfaces. Both of these surfaces are based on CCSD­(T) electronic energies, but the fits display substantial differences in the energies of low-lying stationary points. Little sensitivity to these features is found in the DMC results, which yield zero-point energies based on the two surfaces that differ by between 20 and 30 cm^–1 for all twelve isotopologues of H₅⁺. Likewise, projections of the ground state probability amplitudes, evaluated for the two surfaces, are virtually identical. By using the ground state probability amplitudes, vibrationally averaged rotational constants and dipole moments were calculated. On the basis of these calculations, all isotopologues are shown to be near-prolate symmetric tops. Further, in cases where the ion had a nonzero dipole moment, the magnitude of the vibrationally averaged dipole moment was found to range from 0.33 to 1.15 D, which is comparable to the dipole moments of H₂D⁺ and HD₂⁺. Excited states with up to three quanta in the shared proton stretch and one quantum in the in-phase stretch of the outer H₂ groups were also investigated. Trends in the energies and the properties of these states are discussed

Rotation/Torsion Coupling in H₅⁺, D₅⁺, H₄D⁺, and HD₄⁺ Using Diffusion Monte Carlo

Two methods for studying the rotation/torsion coupling in H₅⁺ are described. The first involves a fixed-node treatment in which the nodal surfaces are obtained from a reduced dimensional calculation in which only the rotations of the outer H₂ groups are considered. In the second, the torsion and rotation dependence of the wave function is described in state space, and the other internal coordinates are described in configuration space. Such treatments are necessary for molecules, like H₅⁺, where there is a very low-energy barrier to internal rotation. The results of the two approaches are found to be in good agreement with previously reported energies for <i>J</i> = 0. The diffusion Monte Carlo treatment allows us to extend the calculations to low <i>J</i>, and results are reported for the three lowest energy torsion excited states with <i>J</i> ≤ 3. For the level of rotational and vibrational excitation investigated, only modest changes in the vibrational wave functions are found. The effects of deuteration are also investigated, focusing on D₅⁺ and the symmetric variants of H₄D⁺ and HD₄⁺

Hierarchically Designed Germanium Microcubes with High Initial Coulombic Efficiency toward Highly Reversible Lithium Storage

Germanium has been investigated intensively for its high specific capacity and tough nature, which make it a promising candidate anode for high energy lithium-ion batteries. However, the rational design of a germanium electrode with enhanced electrochemical performances is still a big challenge. Herein, we designed and synthesized germanium microcubes with a hierarchical structure directly on titanium foil via a simple hydrogen reduction method. An ultrahigh initial Coulombic efficiency of 91.8% was acquired due to the high crystallinity of germanium for reversible lithium insertion and extraction, less adverse side reaction for irreversible lithium loss, and unique hierarchical structure for easier electrolyte penetration. In addition, the Li₂CO₃-predominated solid electrolyte interface contributes significantly to the excellent cycling and rate performances of the anode. Both half and full cell performances demonstrate that germanium has potential applications in high-performance lithium-ion batteries

Kinetics and Structural Changes of Li-Rich Layered Oxide 0.5Li₂MnO₃·0.5LiNi_0.292Co_0.375Mn_0.333O₂ Material Investigated by a Novel Technique Combining in Situ XRD and a Multipotential Step

Li-rich layered oxide 0.5Li₂MnO₃·0.5LiNi_0.292Co_0.375Mn_0.333O₂ was prepared by an aqueous solution–evaporation route. X-ray powder diffraction (XRD) showed that the as-synthesized material was a solid solution consisting of layered α-NaFeO₂-type LiMO₂ (M = Ni, Co, Mn) and monoclinic Li₂MnO₃. The superlattice spots in the selected area electron diffraction pattern indicated the ordering of lithium ions with transition metal (TM) ions in TM layers in this Li-rich layered oxide. Electrochemical performance testing showed that the as-synthesized material could deliver an initial discharge capacity of 267.7 mAh/g, with a capacity retention of 88.5% after 33 cycles. A new combination technique, multipotential step in situ XRD (MPS in situ XRD) measurement, was applied for the first time to investigate the Li-rich layered oxide. Using this approach, the relationships between kinetics and structural variations can be obtained simutaneously. In situ XRD results showed that the <i>c</i> parameter decreased from 3.70 to 4.30 V and increased from 4.30 to 4.70 V, whereas the <i>a</i> parameter underwent a decrease above 4.30 V during the first charge process. Below 3.90 V during the first discharge process, a slight decrease in the <i>c</i> parameter was found along with an increase in the <i>a</i> parameter. During the first charge process, the value of the coefficient of diffusion for lithium ions (<i>D</i>_Li+) decreased to its mininum at 4.55 V, which might be associated with Ni²⁺ migration, as indicated by both Ni occupancy in 3b sites (Ni_3b%) in the Li⁺ layers and complicated chemical reactions. Remarkably, a lattice distortion might occur within the local domain in the host stucture during the first discharge process, indicated by a slight splitting of the (003) diffraction peak at 3.20 V

Insights into Magneto-Optics of Helical Conjugated Polymers

Materials with magneto-optic (MO) properties have enabled critical fiber-optic applications and highly sensitive magnetic field sensors. While traditional MO materials are inorganic in nature, new generations of MO materials based on organic semiconducting polymers could allow increased versatility for device architectures, manufacturing options, and flexible mechanics. However, the origin of MO activity in semiconducting polymers is far from understood. In this paper, we report high MO activity observed in a chiral helical poly-3-(alkylsulfone)­thiophene (<b>P3AST</b>), which confirms a new design for the creation of a giant Faraday effect with Verdet constants up to (7.63 ± 0.78) × 10⁴ deg T^–1 m^–1 at 532 nm. We have determined that the sign of the Verdet constant and its magnitude are related to the helicity of the polymer at the measured wavelength. The Faraday rotation and the helical conformation of <b>P3AST</b> are modulated by thermal annealing, which is further supported by DFT calculations and MD simulations. Our results demonstrate that helical polymers exhibit enhanced Verdet constants and expand the previous design space for polythiophene MO materials that was thought to be limited to highly regular lamellar structures. The structure–property studies herein provide insights for the design of next-generation MO materials based upon semiconducting organic polymers

Facile Synthesis of The Li-Rich Layered Oxide Li_1.23Ni_0.09Co_0.12Mn_0.56O₂ with Superior Lithium Storage Performance and New Insights into Structural Transformation of the Layered Oxide Material during Charge–Discharge Cycle: In Situ XRD Characterization

In this work, the Li-rich oxide Li_1.23N_i0.09Co_0.12Mn_0.56O₂ was synthesized through a facile route called aqueous solution-evaporation route that is simple and without waste water. The as-prepared Li_1.23N_i0.09Co_0.12Mn_0.56O₂ oxide was confirmed to be a layered LiMO₂–Li₂MnO₃ solid solution through ex situ X-ray diffraction (ex situ XRD) and transmission electron microscopy (TEM). Electrochemical results showed that the Li-rich oxide Li_1.23N_i0.09Co_0.12Mn_0.56O₂ material can deliver a discharge capacity of 250.8 mAhg^–1 in the 1st cycle at 0.1 C and capacity retention of 86.0% in 81 cycles. In situ X-ray diffraction technique (in situ XRD) and ex situ TEM were applied to study structural changes of the Li-rich oxide Li_1.23N_i0.09Co_0.12Mn_0.56O₂ material during charge–discharge cycles. The study allowed observing experimentally, for the first time, the existence of β-MnO₂ phase that is appeared near 4.54 V in the first charge process, and a phase transformation of the β-MnO₂ to layered Li_0.9MnO₂ is occurred in the initial discharge process by evidence of in situ XRD pattrens and selected area electron diffraction (SAED) patterns at different states of the initial charge and discharge process. The results illustrated also that the variation of the in situ X-ray reflections during charge–discharge cycling are clearly related to the changes of lattice parameters of the as-prepared Li-rich oxide during the charge–discharge cycles