Double Ionization Dynamics of Molecular Hydrogen in Ultrashort Intense Laser Fields

We experimentally investigate the double ionization pulses. The total kinetic energy release of the two of molecular hydrogen subjected to ultrashort intense laser coincident H＋ ions, which provides a diagnosis of different processes to double ionization of H2, is measured for two different pulse durations, i.e., 25 and 5 fs, and various laser intensities. It is found that, for the long pulse duration （i.e., 25 fs）, the double ionization occurs mainly via two processes, i.e., the charge resonance enhanced ionization and recollision-induced double ionization. Moreover, the contributions from these two processes can be significantly modulated by changing the laser intensity. In contrast, for a few-cycle pulse of 5 fs, only the recollsion-induced double ionization survives, and in particular, this process could be solely induced by the first-return reeollision at appropriate laser intensities, providing an efficient way to probe the sub-laser-cycle molecular dynamics.

Progress in the Use of Molecular Hydrogen for Cancer Treatment

Molecular hydrogen is an effective antioxidant.Numerous studies have demonstrated the therapeutic effects of hydrogen in the treatment of various human diseases.The possibility of using hydrogen in the treatment of cancer was first discovered in 1975,and in recent studies,researchers have reported numerous positive effects of hydrogen in cancer therapy,including:1)the alleviation of complications caused by chemotherapy;2)a reduction of complications caused by radiotherapy;3)delays in the progression of cancer;and 4)enhanced efficacy of conventional therapy when used in combination with hydrogen.This article reviews the research progress in the use of hydrogen in the treatment of cancer,and proposes future directions for research in this field.

Neuroprotective Effects of Molecular Hydrogen:A Critical Review

Molecular hydrogen(H_(2))is a physiologically inert gas.However,during the last 10 years,increasing evidence has revealed its biological functions under pathological conditions.More specifically,H_(2) has protective effects against a variety of diseases,particularly nervous system disorders,which include ischemia/reperfusion injury,traumatic injury,subarachnoid hemorrhage,neuropathic pain,neurodegenerative diseases,cognitive dysfunction induced by surgery and anesthesia,anxiety,and depression.In addition,H_(2) plays protective roles mainly through anti-oxidation,anti-inflammation,antiapoptosis,the regulation of autophagy,and preservation of mitochondrial function and the blood-brain barrier.Further,H_(2) is easy to use and has neuroprotective effects with no major side-effects,indicating that H_(2) administration is a potential therapeutic strategy in clinical settings.Here we summarize the H_(2) donors and their pharmacokinetics.Meanwhile,we review the effectiveness and safety of H_(2) in the treatment of various nervous system diseasesbased on preclinical and clinical studies,leading to the conclusion that H_(2) can be a simple and effective clinical therapy for CNS diseases such as ischemia-reperfusion brain injury,Parkinson's disease,and diseases characterized by cognitive dysfunction.The potential mechanisms involved in the neuroprotective effect of H_(2) are also analyzed.

Molecular hydrogen is a promising therapeutic agent for pulmonary disease

Molecular hydrogen exerts biological effects on nearly all organs. It has anti-oxidative, anti-inflammatory, and anti-aging effects and contributes to the regulation of autophagy and cell death. As the primary organ for gas exchange, the lungs are constantly exposed to various harmful environmental irritants. Short-or long-term exposure to these harmful substances often results in lung injury, causing respiratory and lung diseases. Acute and chronic respiratory diseases have high rates of morbidity and mortality and have become a major public health concern worldwide. For example, coronavirus disease 2019(COVID-19) caused by severe acute respiratory syndrome coronavirus 2(SARS-CoV-2) has become a global pandemic. An increasing number of studies have revealed that hydrogen may protect the lungs from diverse diseases, including acute lung injury,chronic obstructive pulmonary disease, asthma, lung cancer, pulmonary arterial hypertension, and pulmonary fibrosis. In this review, we highlight the multiple functions of hydrogen and the mechanisms underlying its protective effects in various lung diseases, with a focus on its roles in disease pathogenesis and clinical significance.

Molecular mechanics and dynamics simulation of hydrogen diffusion in aluminum melt

The main impurities in aluminum melt are hydrogen and Al_2O_3,which can deteriorate melt quality and materials performance.However,the diffusion process of H atoms in aluminum melt and the interactions among Al atoms,Al_2O_3 and hydrogen have been studied rarely.Molecular mechanics and dynamics simulations are employed to study the diffusion behaviors of different types of hydrogen,such as free H atoms,H atoms in H_2 and H^+ions in H_2O using COMPASS force field.Correspondingly,force field types h,h1h and h1o are used to describe different types of hydrogen which are labeled as H_h,H_(h1h) and H_(h1o).The results show that the adsorption areas are maximum for H_(h1o),followed by H_(h1h) and H_h.The diffusion ability of H_(h1o) is the strongest whereas H_h is hard to diffuse in aluminum melt because of the differences in radius and potential well depth of various types of hydrogen.Al_2O_3 cluster makes the Al atoms array disordered,creating the energy conditions for hydrogen diffusion in aluminum melt.Al_2O_3 improves the diffusion of H_h and H_(h1o),and constrains H_(h1h) which accumulates around it and forms gas porosities in aluminum.H_(h1o) is the most dispersive in aluminum melt,moreover,the distance of Al-H_(h1o) is shorter than that of Al-H_(h1h),both of which are detrimental to the removal of H_(h1o).The simulation results indicate that the gas porosities can be eliminated by the removal of Al_2O_3 inclusions,and the dispersive hydrogen can be removed by adsorption function of gas bubbles or molten fluxes.

Molecular Dynamics Simulation and Experimental Proof of Hydrogen-enhanced Dislocation Emission in Nickel

A quasi three dimensions molecular dynamic method was used to simulate the effect of hydrogen on dislocation emission and crack propagation in nickel. In situ observation in a transmission electron microscope (TEM) was used to confirm the simulation results. The simulation result indicated that hydrogen solubilized in nickel decreased the critical stress intensity for the dislocation emission, i.e., hydrogen enhanced dislocation emission. In situ observation in TEM showed that hydrogen enhanced dislocation emission and motion before the initiation of hydrogen-induced crack.

Catalytic Hydrogenation over Palladium Complex of Molecular Complex of Poly(4-vinylpyridine) with Acetic Acid

The palladium complex of the molecular complex of poly(4 vinylpyridine) with acetic acid(PVP/ HAc Pd) was prepared. Its catalytic activity for the hydrogenation of nitrobenzene was found much higher than that of the corresponding palladium complex of poly(4 vinylpyridine). In the presence of a strong inorganic alkali, especially potassium hydroxide, the catalytic activity is greatly improved. The suitable hydrogenation condition for PVP/HAc Pd is to use 0 1 mol/L ethanol solution of potassium hydroxide as the hydrogenation medium and the hydrogenation is carried out at 45 ℃.

Molecular Simulation of Hydrogen Adsorption Density in Single-Walled Carbon Nanotubes and Multilayer Adsorption Mechanism

The adsorption of hydrogen onto single-walled carbon nanotubes (SWCNTs) was studied by molecular dynamics (MD) sim'lation. It was found that the hydrogen molecules distribute regularly inside and outside of the tube. Density distribution was computed for H2 molecule. Theoretical analysis of the result showed the multilayer adsorption mechanism of SWCNTs. The storage of H2 in SWCNTs is computed, which provides essential theoretical reference for further study of hydrogen adsorption in SWCNTs.

Influence of a strong magnetic field on the hydrogen molecular ion using B-spline-type basis-sets

As an improvement on our previous work [J. Phys. B： At. Mol. Opt. Phys. 45 085101（2012）], an accurate method combining the spheroidal coordinates and B-spline basis is applied to study the ground state 1σg and low excited states1σu, 1πg,u, 1δg,u, 2σg of the H＋2in magnetic fields ranging from 10^9Gs（1 Gs = 10^-4T） to 4.414 × 10^13 Gs. Comparing the one-center method used in our previous work, the present method has a higher precision with a shorter computing time.Equilibrium distances of the states of the H＋2in strong magnetic fields were found to be accurate to 3-5 significant digits（s.d.） and the total energies 6-11 s.d., even for some antibonding state, such as 1πg, which is difficult for the one-center method to give reliable results while the field strength is B ≥ 10^13 Gs. For the large disagreement in previous works, such as the equilibrium distances of the 1πg state at B = 10^9 Gs, the present data may be used as a reference. Further, the potential energy curves（PECs） and the electronic probability density distributions（EPDDs） of the bound states 1σg, 1πu, 1δg and antibonding states 1σu, 1πg, 1δu for B = 1, 10, 100, 1000 a.u.（atomic unit） are compared, so that the different influences of the magnetic fields on the chemical bonds of the bound states and antibonding states are discussed in detail.

Diffusion behavior of hydrogen isotopes in tungsten revisited by molecular dynamics simulations

Molecular dynamics simulations were performed to study the diffusion behavior of hydrogen isotopes in single-crystal tungsten in the temperature range of 300-2000 K. The simulations show that the diffusion coefficient of H isotopes exhibits non-Arrhenius behavior, though this deviation from Arrhenius behavior is slight. Many-body and anharmonic effects of the potential surface may induce slight isotope-dependence by the activation energy; however, the dependence of the pre-factor of the diffusion coefficient on the isotope mass is diminished. The simulation results for H-atom migration near W surfaces suggest that no trap mutations occur for H atoms diffusing near either W{ 100} or W{ 111 } surfaces, in contrast to the findings for He diffusion near W surfaces. Based on the H behavior obtained by our MD simulations, the time evolution of the concentration distribution of interstitial H atoms in a semi-infinite W single crystal irradiated by energetic H projectiles was calculated. The effect of H concentration on H diffusion is discussed, and the applicability of the diffusion coefficients obtained for dilute H in W is assessed.

High-precision spectroscopy of hydrogen molecular ions

In this paper, we overview recent advances in high-precision structure calculations of the hydrogen molecular ions （H2＋ and HD＋）, including nonrelativistic energy eigenvalues and relativistic and quantum electrodynamic corrections. In combination with high-precision measurements, it is feasible to precisely determine a molecular-based value of the proton- to-electron mass ratio. An experimental scheme is presented for measuring the rovibrational transition frequency （v,L） ： （0, 0） → （6,1） in HD＋, which is currently underway at the Wuhan Institute of Physics and Mathematics.

Hydrogen Promoted Decomposition of Ammonium Dinitramide:an ab initio Molecular Dynamics Study

Thermal decomposition of a famous high oxidizer arnrnoniurn dinitrarnide （ADN） under high temperatures （2000 and 3000 K） was studied by using the ab initio molecular dynamics method. Two different ternperature-dependent initial decomposition mechanisms were observed in the unirnolecular decomposition of ADN, which were the intrarnolecular hydrogen transfer and N-NO2 cleavage in N（NO2） . They were competitive at 2000 K, whereas the forrner one was predominant at 3000 K. As for the rnultimolecular decomposition of ADN, four different initial decomposition reactions that were also ternperature-dependent were observed. Apart from the aforernentioned rnechanisrns, another two new reactions were the interrnolecular hydrogen transfer and direct N-H cleavage in NH4＋. At the temperature of 2000 K, the N-NO2 cleavage competed with the rest three hydrogen-related decomposition reactions, while the direct N-H cleavage in NH4＋ was predominant at 3000 K. After the initial decomposition, it was found that the temperature increase could facilitate the decomposition of ADN, and would not change the key decomposition events. ADN decomposed into small molecules by hydrogen-prornoted simple, fast and direct chemical bonds cleavage without forrning any large intermediates that rnay impede the decomposition. The main decomposition products at 2000 and 3000 K were the same, which were NH3, NO2, NO, N2O, N2, H2O, and HNO2.

Ab initio path-integral molecular dynamics and the quantum nature of hydrogen bonds

The hydrogen bond （HB） is an important type of intermolecular interaction, which is generally weak, ubiquitous, and essential to life on earth. The small mass of hydrogen means that many properties of HBs are quantum mechanical in nature. In recent years, because of the development of computer simulation methods and computational power, the influence of nuclear quantum effects （NQEs） on the structural and energetic properties of some hydrogen bonded systems has been intensively studied. Here, we present a review of these studies by focussing on the explanation of the principles underlying the simulation methods, i.e., the ab initio path-integral molecular dynamics. Its extension in combination with the thermodynamic integration method for the calculation of free energies will also be introduced. We use two examples to show how this influence of NQEs in realistic systems is simulated in practice.

Molecular Dynamics Study on the Diffusion Properties of Hydrogen Atoms in Bulk Tungsten

Molecular dynamics simulations were performed to study the diffusion behavior of hydrogen atoms in body-centered cubic（bcc） tungsten（W）. The energy distribution of a single hydrogen atom in the （001） plane of tungsten lattice was computed. The values of diffusion barriers agree well with other theoretical and experimental results. The interaction between an H atom and a vacancy was simulated, which shows effect on the diffusion behavior of hydrogen an H atom to diffuse in bulk W with and evidence of strong binding effect. The temperature atoms was investigated. The critical temperature for without vacancies were calculated to be 950 K and 450 K, respectively, which is supported by several experimental results. In addition, the diffusion coefficient of hydrogen atoms in tungsten was evaluated and analyzed.

Hydrogen Diffusion in Aluminum Melts: An ab initio Molecular Dynamics Study

The diffusion process of hydrogen in aluminum melts was investigated by molecular dynamics simulation. The pair correlation function, first peak position, and coordination number was calculated and differences in the structural properties among Al-H, Cl-H, and Al-Cl pair were examined. The mechanism of chlorine on improving hydrogen diffusion was discussed. From an ab initio molecular dynamics calculations, the diffusivity of hydrogen in liquid aluminum as D（T）=（0.118×10-4 m2/s）exp（-0.316 eV/kT） is obtained, which is in good agreement with the experimental data. Correspondingly the diffusivity with presence of chlorine is promoted as D（T）=（0.09×10-4 m2/s）exp（-0.251 eV/kT）. It can be concluded that the diffusion of hydrogen in aluminum melts can be enhanced in the presence of chlorine.

Molecular Statics Simulation of Hydrogen Defect Interaction in Tungsten

Hydrogen （H） defect interactions have been investigated by molecular statics sim- ulations in tungsten （W）, including H-H interactions and interactions between H and W self- interstitial atoms. The interactions between H and small H-vacancy clusters are also demonstrated; the binding energies of an H, a vacancy and a self-interstitial W to an H-vacancy cluster depend on the H-to-vacancy ratio. We conclude that H bubble formation needs a high concentration of H in W for the H bubble nucleation and growth, which are also governed by the H-to-vacancy ratio of the cluster. The vacancy first combines with H atoms and a cluster forms, then the H-vacancy cluster goes through the whole process of vacancy capture, H capture, and vacancy capture again, and as a result the H-vacancy cluster grows larger and larger. Finally, the H bubble forms.

Molecular dynamics simulation of atomic hydrogen diffusion in strained amorphous silica

Understanding hydrogen diffusion in amorphous SiO2(a-SiO2),especially under strain,is of prominent importance for improving the reliability of semiconducting devices,such as metal-oxide-semiconductor field effect transistors.In this work,the diffusion of hydrogen atom in a-SiO2 under strain is simulated by using molecular dynamics(MD)with the ReaxFF force field.A defect-free a-SiO2 atomic model,of which the local structure parameters accord well with the experimental results,is established.Strain is applied by using the uniaxial tensile method,and the values of maximum strain,ultimate strength,and Young's modulus of the a-SiO2 model under different tensile rates are calculated.The diffusion of hydrogen atom is simulated by MD with the ReaxFF,and its pathway is identified to be a series of hops among local energy minima.Moreover,the calculated diffusivity and activation energy show their dependence on strain.The diffusivity is substantially enhanced by the tensile strain at a low temperature(below 500 K),but reduced at a high temperature(above 500 K).The activation energy decreases as strain increases.Our research shows that the tensile strain can have an influence on hydrogen transportation in a-SiO2,which may be utilized to improve the reliability of semiconducting devices.

MOLECULAR DYNAMICS SIMULATION ON VIERATIONAL SPECTROSCOPIC FEATURES OF HYDROGEN BONDS IN CRYSTALLINE POLYMERS

Introduction The molecular dynamics simulation technique has recently proved to be a suitable alternative approachfor simulation of vibrational spectroscopy. In this study, molecular dynamics was utilized to understandlow frequency vibrations in highly ordered poly(ρ-phenylene terephthalmide) (PPTA). A key structuralfeature of this polymer is the presence of hydrogen bonds. There is little question that this strong localized

Spectroscopic Characterization, Molecular Modeling and DFT/TD-DFT/PCM Calculations of Novel Hydrogen-Bonded Charge Transfer Complex between Chloranilic Acid and 2-Amino-4,6-Dimethylpyridine

A charge transfer hydrogen bonded complex between the electron donor (proton acceptor) 2-amino-4,6-dimethylpyridine with the electron acceptor (proton donor) chloranilic acid has been synthesized and studied experimentally and theoretically. The stability constant recorded high values indicating the high stability of the formed complex. In chloroform, ethanol, methanol and acetonitrile were found the stoichiometric ratio 1:1. The solid complex was prepared and characterized by different spectroscopy techniques. FTIR, 1H and 13C NMR studies supported the presence of proton and charge transfers in the formed complex. Complemented with experimental results, molecular modelling using the density functional theory (DFT) calculations was carried out in the gas, chloroform and methanol phases where the existence of charge and hydrogen transfers. Finally, a good consistency between experimental and theoretical calculations was found confirming that the applied basis set is the suitable one for the system under investigation.

Studies on the Structures and Hydrogen-bonding Interactions in Aqueous Glycine Solutions Using All-atom Molecular Dynamics Simulations and NMR Spectroscopy

All-atom molecular dynamics （MD） simulations and chemical shifts were used to study interactions and structures in the glycine-water system. Radial distribution functions and the hydrogen-bond network were applied in MD simulations. Aggregates in the aqueous glycine solution could be classified into different regions by analysis of the hydrogen-bonding network. Temperature-dependent NMR spectra and the viscosity of glycine in aqueous solutions were measured to compare with the results of MD simulations. The variation tendencies of the hydrogen atom chemical shifts and viscosity with concentration of glycine agree with the statistical results of hydrogen bonds in the MD simulations.