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.

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.

Unimolecular Dissociation of H⁺<sub style="margin-left:-6px;">2n+1</sub>Hydrogen Clusters: Measured Cross Sections and Theoretically Calculated Rate Constants

In this paper, we studied the process of dissociation unimolecular of the evaporation of H+2n+1 hydrogen clusters according to size, using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The rate constants k(E) were determined with the use of statistical theory of unimolecular reactions using various approximations. In our work, we used the products frequencies instead of transitions frequencies in the calculation of unimolecular dissociation rates obtained by three models RRKM. The agreement between the experimental cross section ratio and calculated rate ratio with direct count approximation seems to be reasonable.

Drag reduction and shear resistance properties of ionomer and hydrogen bond systems based on lauryl methacrylate

Based on molecular dynamics simulation results, a lauryl methacrylate polymer with drag reduction and shear resistance properties was designed, and synthesized by emulsion polymerization using 2-vinyl pyridine and methyl methacrylate as the polar polymerization monomer. After ionization of lauryl methacrylate polymer, an ion-dipole interaction based drag reduction agent （DRA） was obtained. The existence of ion-dipole interaction was proven through characterization of the drag-reducing agent from its infrared （IR） spectrum. The pilot-scale reaction yield of the DRA under optimum conditions was investigated, and the drag reduction and shear resistance properties were measured. The results show that： l） The ion-dipole or hydrogen bonding interaction can form ladder-shaped chains, therefore the synthesized DRA has shear resistance properties; 2） The larger the molecular weight （MW） and more concentrated the distribution of MW, the better the drag reduction efficiency and the performance of the ionomer system was superior to that of the hydrogen bonding system; 3） With increasing shear frequency, the drag-reduction rates of both the DRAs decreased, and the drag reduction rate of the ionomer system decreased more slowly than of the corresponding hydrogen bonding system. From the point of view of drag reduction rate and shear resistance property, the ionomer system is more promising than the hydrogen bonding system

Effects of Mg2+ on the binding of the CREB/CRE complex:Full-atom molecular dynamics simulations

Metal ions play critical roles in the interaction between deoxyribonucleic acid(DNA) and protein.The experimental research has demonstrated that the Mg^2+ ion can affect the binding between transcription factor and DNA.In our work,by full-atom molecular dynamic simulation, the effects of the Mg^2+ ion on the cyclic adenosine monophosphate(cAMP)response element binding protein(CREB)/cAMP response elements(CRE) complex are investigated.It is illustrated that the number of hydrogen bonds formed at the interface between protein and DNA is significantly increased when the Mg^2+ ion is added.Hence, an obvious change in the structure of the DNA is observed.Then the DNA base groove and base pair parameters are analyzed.We find that, due to the introduction of the Mg2+ ion, the DNA base major groove becomes narrower.A potential mechanism for this observation is proposed.It is confirmed that the Mg^2+ ion can enhance the stability of the DNA–protein complex.

Molecular Axis Orientation in Charge Transfer Reactions Determined with a Reaction Microscope

Based on the reaction microscope at the institute of modern physics, the reaction mechanism in molecular ion-atom collisions is investigated experimentally. The features of this system is illustrated by a kinematically complete experhnent performed for the collision process. Using the so-called list-mode data recording technique and the coincidence measurement, the momentum vector of each fragment from the molecular ion were recorded event by event. The orientation of the molecular axis for H2^＋ dissociation reactions could be determined for each event in the off-line analysis. The measured orientation of the molecular ion is believed the same as the one at the instance of collision under axial recoil approximation. The polar angle resolution of the molecular orientation of ±8° was obtained.

Triatomic wake effect and the determination of the molecular structure of HD_2^+ from the Coulomb explosion

A new theoretical model of the triatomic molecular wake effect is proposed and applied to molecular ions D^＋3 and HD^＋2 while passing through a solid. The wake effects resulting from the reactions of the two similar ions with thin carbon foil are also investigated by using the Coulomb explosion technique. The experimental results are in good agreement with theoretical estimates and the molecular structure of HD^＋2 is determined by using the model.

氢分子离子超精细结构理论综述

通过氢分子离子振转光谱的高精度实验测量和理论计算,可以精确确定基本物理常数,如质子-电子质量比、氘核-电子质量比、里德伯常数、以及质子和氘核的电荷半径.氢分子离子光谱包含丰富的超精细结构,为了从光谱中提取物理信息,我们不仅需要研究振转光谱跃迁理论,还需要研究超精细结构理论.本文回顾了氢分子离子精密光谱的实验和理论研究历程,着重介绍了氢分子离子超精细结构的研究历史和现状.在20世纪的下半叶就有了关于氢分子离子超精细劈裂的领头项Breit-Pauli哈密顿量的理论.随着21世纪初非相对论量子电动力学(NRQED)的发展,氢分子离子超精细结构的高阶修正理论也得到了系统的发展,并于最近应用到H_(2)^(+)和HD^(+)体系中,其中包括mα^(7) ln(α)阶量子电动力学(QED)修正.对于H_(2)^(+),超精细结构理论计算经过数十年的发展,可以与20世纪的相应实验测量符合.对于HD^(+),最近发现超精细劈裂实验测量和理论计算存在一定的偏差,且无法用mα^(7)阶非对数项的理论误差来解释.理解这种偏差一方面需要更多的实验来相互检验,另一方面对理论也需要进行独立验证并发展mα^(7)阶非对数项理论以进一步减小理论误差.

氢分子离子HD^+的薛定谔方程的求解方法

从实验室坐标系下的氢分子离子HD+的哈密顿算符出发,考虑到原子核的运动以及电子与原子核之间的相互作用,讨论异核和同核氢分子离子HD+的薛定谔方程的Born-Oppenheimer近似求解方法和绝热近似求解方法,同时展示四种展开波函数的方法,其中包括B-splines技术的应用.

异核氢分子离子HD^+在磁场中的哈密顿量

考虑原子核的运动,通过球极坐标和直角坐标向椭球坐标的变换,采用特殊的变换方法,对平行磁场中的异核氢分子离子HD+的哈密顿量进行推导,同时构造出绝热厄密共轭哈密顿算符.

Semi-classical explanation for the dissociation control of H_2^+

A semi-classical model is utilized to explain the dissociation control of the hydrogen molecular ion （H^-）. By ana- lyzing the curve of the dissociation asymmetry parameter as a function of the time delay between the exciting and steering pulses, we find that the dissociation control is dependent not only on the peak intensity and direction of the electric field of the steering pulse, but also on the peak intensity of the exciting pulse.

Deflections of photoelectron classical trajectories in screened Coulomb potentials of H_2^+

The photoelectron momentum distribution of H＋ in circularly polarized laser fields is studied based on classical trajectory calculations. We screen Coulomb potentials at different radii, and trace trajectories of an ensemble of electrons in such screened Coulomb potentials and circularly polarized laser fields. Simulations show that electron trajectories are bent by Coulomb fields, resulting in the laser-intensity-dependent drift of photoelectron momentum distributions in the laser polarization plane. This study intuitively explains how Coulomb potentials modify photoelectron momenta.

Surface-Induced Dissociation of Low Energy H_2^(+) Impact on a Carbon Surface: A Monte Carlo Simulation

A Monte Carlo simulation based on the classical binary collision approximation is performed to investigate the interaction of W2 ions with the carbon target. The incident H2^＋ ion is characterized by its translational energy, eigenenergy and population of the vibrational state, and orientation of the ion with respect to the target surface. It is shown that experimentally determined energy resolved mass spectrum of H＋ can be nicely reproduced with the help of the proposed model. These simulations predict that translational to vibrational （T → V） energy transfer efficiency increases nonlinearly with translational energy of the incident ion. T → V energy transfer efficiency along with the initial vibrational energy of the incident H＋ ion found to play an important role in dissociation. Our simulations also show that the fraction of absorbed, reflected, and dissociated ions depends on the translational energy. The average vibrational energy of reflected H＋ increases with its initial translational energy. Moreover, average number of collisions required for dissociation varies inversely with the initial translational energy of the H2^＋.

Control of electron localization in the dissociation of H_(2)^(+)and its isotopes with a THz pulse

The molecular dissociation with a two-laser-pulse scheme is theoretically investigated for the hydrogen molecular ion（H2^＋） and its isotopes（HD^＋and HT^＋）. The terahertz pulse is used to steer the electron motion after it has been excited by an ultrashort ultraviolet laser pulse and an unprecedented electron localization ratio can be achieved. With the coupled equations, the mass effect of the nuclei on the effective time of the electron localization control is discussed.

Mechanistic Insights into Structural Stability of the Selectivity Filters in Typical Cation Channels

The reliable functioning of ion channels should be closely related to their structural stability. The selectivity filter in the KcsA potassium channel possesses four stable ion binding sites that can coordinate nearly fully dehydrated ions, whereas only two of such binding sites exist in the non-selective NaK channel, and none of them is found in the NavAb sodium channel. Here we show that the stability of the selectivity filters in these tetrameric cation channels is inversely correlated with the number of stable binding sites by extensive molecular dynamics simulations. While the presence of coordinated ions is crucial for the selectivity filters of the KcsA and NaK channels to stabilize the conformations in their crystal structures, the selectivity filter of the NavAb channel shows higher stability, independent of the presence of ions. We further show that the distinct repulsive electrostatic interactions between negatively charged oxygen atoms in the selectivity filter which form the stable binding sites are responsible for the different stability of these cation channels. The hydrogen bonding networks between residues in the selectivity filter and its adjacent pore helix also play an important role in maintaining stability. Together, these results provide important mechanistic insights into the structural stability of the selectivity filters in typical cation channels.

氢迁移诱导碳氢分子碎裂动力学研究进展

氢迁移反应是最基本、最重要的化学反应之一,它的发生可诱发碳氢分子产生特殊的碎裂通道,表现出独特的动力学特征。近些年来,随着实验技术以及理论手段的发展,对碳氢分子解离中氢迁移过程背后微观物理机制的理解逐步深化完善。本文以参与碳氢分子解离的氢迁移过程为综述对象,简要介绍了研究氢迁移动力学的实验和理论方法,总结了当前对C_(2)H_(2)、C_(2)H_(4)以及C_(2)H_(6)等碳氢分子解离产生碳碳键对称/非对称断裂通道和H_(3)^(+)离子形成通道的机制的认识,并对后续研究内容作出展望。

双色激光场中1维共线氢分子离子的经典动力学研究

运用经典理论方法,并采用辛算法数值求解了双色激光场作用下1维共线氢分子离子(H2+)的哈密顿正则方程,得到了氢分子离子在激光场下的经典轨迹。计算了单色场和双色场下氢分子离子(H2+)的存活几率、电离几率、解离几率、库仑爆炸几率随时间的演化,分析了双色场的相位、强度、强度比及倍频的变化对氢分子离子动力学行为的影响,并给出了相应的物理解释。

激光场中一维和三维氢分子离子模型经典动力学行为的比较

应用经典轨迹方法,采用辛算法数值求解激光场中的一维和三维氢分子离子(H2+)的Hamilton正则方程,得到氢分子离子在激光场作用下的经典轨迹,并比较分析氢分子离子一维模型与三维模型的存活、解离、电离和库仑爆炸等动力学行为,以及电子的运动情况的相似之处.数值结果表明,采用一维模型能近似定性反映氢分子离子的动力学行为,并且简便可行.

氢分子离子量子点能级的量子尺寸效应

用B样条技术计算氢分子离子量子点能级的量子尺寸效应.计算结果显示:当R较小时,能级随R的增加快速下降,量子尺寸效应明显.当R较大时,能级变化速度变缓,量子尺寸效应减弱.当R较小时,E1——D/R曲线上升快;当R较大时,E1——D/R曲线上升变慢.当m=0时,能级对D/R的变化很敏感.当m≥1时,m越大,能量对D/R的变化越不敏感.

铵根离子在水溶液中的跳跃转动机理（英文）

铵根离子的动力学行为与生命体内的生物和化学过程密切相关.依据流体力学理论,由于铵根离子与水分子之间存在多个强氢键,其转动应较慢,但实验结果并非如此,其转动的微观机理尚不清晰.本文分子动力学模拟研究表明,水溶液中铵根离子主要以快速、大角度的跳跃方式进行转动,像水分子一样遵从扩展分子跳跃转动模型.通过微观转动模式的分解和两种转动弛豫时间的比较发现,相对其氢键骨架的扩散转动,跳跃转动对其转动速率贡献更大,并随浓度增大不断强化.与水分子氢键交换方式相比,铵根离子更倾向于在非氢键相连的水分子间发生交换.