Plasma Processes Driven by Current Sheets and Their Relevance to the Auroral Plasma

Satellite and rocket observations have revealed a host of auroral plasma processes, including large dc perpendicular electric fields (E?) associated with electrostatic shocks, relatively weak parallel electric fields (E?) associated with double layers, upflowing ions in the form of beams and conics, downflowing and upflowing accelerated electron beams, several wave modes such as the electrostatic ion-cyclotron (EIC), lower hybrid (LH), very low frequency (VLF), extremely low frequency (ELF), and high-frequency waves and associated nonlinear phenomena. Recently, we have attempted to simulate the various processes using a two-dimensional particle-in-cell code in which the plasma is driven by current sheets of a finite thickness. Striking similarities between the observed auroral plasma processes and those seen in the simulations are found. In this paper we give a review of the plasma processes dealing with dc and ac electric fields, formation of ion beams and conics, and electron acceleration. Electrostatic shock-type electric fields (E?e) occur near the current sheet edges. Such fields arise because of the contact between the high-and low-density plasmas inside and outside the sheet, respectively. Double layers having upward electric fields form inside the sheet and they are distinguishable from the large perpendicular electric fields (E?e) only in wide sheets with thicknesses l >> ?i, the ion Larmor radius. Double layers with a reverse polarity form outside the sheet where downward currents flow. The most energetic ions are found to have pitch angles near 90°, implying a large perpendicular acceleration of the ions.     

Acoustic double layers in multispecies plasma

Particle simulation in a one-dimensional bounded system is used to examine the formation of acoustic double layers in the presence of two ion species. Double-layer formation depends critically on the details of the distribution functions of the supporting ion populations, and their relative drifts with respect to the electrons. The effect of having two ion components, an H⁺ and an O⁺ beam, on double-layer evolution from ion acoustic turbulence driven by an electron drift relative to the H⁺ beam of ≈0.5u _e, where uu_e is the electron thermal speed, is examined. The ratio of ion drifts is taken to be consistent with acceleration by a quasi-static auroral potential drop (i.e. V _H/V_O=√M_O/ M_H=4.0). Acoustic double layers form in either ion species on the time scale τ≈100ω_ps^-1, where ω_ps is the ion plasma frequency for species `s' and s=H or O, and for drifts relative to the electrons lower than that required for double layer formation in simulations of single ion component plasma     

Rescattering double ionization of D2 and H2 by intense laser pulses

We have measured momentum spectra and branching ratios of charged ionic fragments emitted in the double ionization of D2 (and H2) molecules by short intense laser pulses. We find high-energy coincident D+ (and H+) ion pairs with kinetic energy releases between 8 and 19 eV which appear for linearly polarized light but are absent for circularly polarized light. The dependence on the polarization, the energy distributions of the ions, and the dependence on laser intensity of yield ratios lead us to interpret these ion pairs as due to a rescattering mechanism for the double ionization. A quantitative model is presented which accounts for the major features of the data.     

Dipole moment of PH+ and the atomic masses of 28Si, 31P by comparing cyclotron frequencies of two ions simultaneously trapped in a penning trap

By trapping pairs of ions in a Penning trap, alternating each ion between large and small cyclotron orbits, we have measured the cyclotron frequency ratios 12C2H4+/28Si+, 13C2H2+/28Si+, 28SiH3+/31P+, and 16O2+/31PH+, all to <30 ppt precision. The 16O2+/31PH+ data exhibit a bimodal distribution due to the polarizability of the Lambda-doubling components of the PH+ ground state, from which we obtain the electric dipole moment of 31PH+, 0.331(8) ea0. Combined with other atomic mass measurements we also obtain improved values for m(28Si), 27.976 926 535 0(6) u, and m(31P), 30.973 761 998 9(9) u.     

V5+掺杂TiO2金红石结构的分子动力学

采用经典离子晶体相互作用势模型， 进行量子化修正，对TiO2金红石相替位式掺杂0.5mol％V5+进行分子动力学模拟，计算了常温常压下的键长、键角的分布函数，分析了晶体的微结构变化以及V5+对TiO6八面体的影响．模拟结果表明，掺杂V5+会导致Ti-O、O-O键长以及O-Ti-O键角的分布范围变宽，其中，键长的主峰位置未发生显著的移动， 而键角主峰向低角度方向移动． 由于V5+比Ti4+有较高的正电荷和较小的离子半径， 因此V5+向氧八面体间空隙扩散，且掺杂V5+迁移出原来的O6八面体，从而导致空隙邻近的TiO6八面体发生严重扭曲．在低掺杂情况下(0.5 mol％)虽然掺杂易造成结构畸变，但模拟体系整体仍维持金红石结构；所得模拟的键长变化、掺杂V5+迁移、晶相等结构特性与FTIR、Raman、XRD、ESR等实验结果相一致．     

Drift-kinetic Alfvén waves observed near a reconnection X line in the earth's magnetopause

We identify drift-kinetic Alfvén waves in the vicinity of a reconnection X line on the Earth's magnetopause. The dispersive properties of these waves have been determined using wavelet interferometric techniques applied to multipoint observations from the Cluster spacecraft. Comparison of the observed wave dispersion with that expected for drift-kinetic Alfvén waves shows close agreement. The waves propagate outwards from the X line suggesting that reconnection is a kinetic Alfvén wave source. Energetic O+ ions observed in these waves indicate that reconnection is a driver of auroral ion outflow.     

H3O+, NO+和O+·2离子同九种烷氧基醇化合物反应的研究

在用选择离子流动管质谱(SIFT-MS)分析常用指甲油清洗垫发现大量4-丁酸内脂(γ-butyrolactone, GBL)和2-丁氧基乙醇(2-butoxy-1-ethanol)等挥发性气体后, 运用选择离子流动管(SIFT)对H3O , NO 和O ·2离子同九种烷氧基醇化合物(R1-O-R2OH)之间的反应进行了研究. 获得了这些反应在潮湿空气条件下进行的情况, 并运用产物离子水合物的种类和分布来确认产物离子的结构和反应机理. 还研究了在不同载气压力下进行的反应. 结果表明, 这些化合物同H3O 和NO 的反应都是先生成初生态离子-分子络合物, (H3O .M)*和(NO .M)*, 然后经不同反应渠道生成各种离子产物. 这些初生态络合物同反应体系中存在的气体分子(如氦气, 氮气和氧气分子)的碰撞对最终离子产物的形成和分布也有影响. 这些化合物同O2 ·反应会生成各种离解碎片离子, 但不能确定这些离子是否经由初生态络合物(O2 ·.M)*生成. 该项研究提供了用SIFT-MS在空气和潮湿气体中分析这些化合物所需的反应速率常数和离子产物等动力学数据, 并将进一步应用到药物成瘾及滥用和呼吸道疾病的诊断和分析等领域.     

一维硫酸镉-双咪唑配合物的合成、结构及谱学性质研究

采用水热合成的方法,得到一种新颖镉的配合物{[Cd(H2biim)2(SO4)].3H2O}n(1,H2biim=2,2’-biimidazole)。通过X-ray单晶衍射分析可知,在该化合物中,SO24-桥连Cd(Ⅱ)离子在c轴上形成"之"字形一维无机CdSO4链。双咪唑配体通过与镉的配位作为支链悬挂在链的两侧,链与链之间分别通过π—π堆积和氢键作用,拓展为三维超分子网络。二维红外相关光谱分析表明SO24-的对称伸缩振动及咪唑环上的N—C伸缩和反伸缩振动,以及NC伸缩振动对热微扰均有响应。稳态荧光分析显示,配合物在397nm光激发下,在498nm处出现了强的蓝光,该发射带归属为配体到金属的荷移跃迁。     

Classical Effects of Carrier--Envelope Phase on Nonsequential Double Ionization

A classical microcanonical 1＋1-dimensional model is used to investigate the ion momentum distributions in nonsequential double ionization with linearly polarized few-cycle pulses. We find that the ion momentum distribution has a strong dependence on the carrier-envelope phase of the few-cycle pulse, which is consistent with the experimental results qualitatively. Back analysis shows that the ionization probability of the first electron at different phases and its returning kinetic energy play the main role on the ion momentum distributions.     

Ion conics and counterstreaming electrons generated by lower hybridwaves in the Earth's magnetosphere

The exotic phenomenon of energetic ion-conic and counterstreaming electron formulation by lower hybrid waves along the discrete auroral field lines in the Earth's magnetosphere is considered. Mean particle calculations, plasma simulations, and analytical treatments of the acceleration processes are described. It is shown that, in the primary auroral electron-beam region, lower hybrid waves could be an efficient mechanism for the transverse heating of ions of ionospheric origin (H ⁺ and O⁺) as well as for the field-aligned heating of the ambient electrons leading to coincident counterstreaming electron distributions. For oxygen ions to be energized by such a wave-particle interaction process, however, some sort of preheating mechanism will be required     

稀土配合物RE(TPTZ)Cl_3的合成、表征及荧光性能研究

首次以2,4,6-三吡啶基三嗪（TPTZ）与Sm, Eu, Tb和Dy氯化物反应,合成四种单一稀土配合物以及Tb分别1∶1掺Gd, Y, La的三种异核配合物。经元素分析、稀土络合滴定、摩尔电导率、红外光谱、紫外光谱和差热-热重测定表明,配合物的组成分别为RE（TPTZ）Cl3&#183;3H2O（RE=Sm, Eu, Tb, Dy）和Tb0.5Ln0.5（TPTZ）Cl3&#183;3H2O（Ln=Gd, Y, La）;TPTZ作为三齿配体与稀土离子配位,即中心环提供一个N原子,两个吡啶环分别提供一个N原子;配合物中3个水分子与稀土离子配位,1个Cl-在外界,2个在内界,为1∶1型电解质;配合物内外界可能为[RE（TPTZ）（H2O）3Cl2] Cl,稀土离子的配位数为8。配合物的荧光光谱测试表明,四种单一稀土配合物中,Tb配合物发光最强;三种1∶1掺杂异核Tb配合物荧光强度大于纯Tb配合物,表明Y3＋, La3＋和Gd3＋都可以敏化Tb3＋的发光,其中Gd3＋的敏化作用最强,Y3＋次之,La3＋最差。     

Total, partial, and electron-capture cross sections for ionization of water vapor by 20-150 keV protons

We present experimental results for proton ionization of water molecules based on a novel event by event analysis of the different ions produced (and lost). We are able to obtain mass analyzed product ion signals (e.g., H2O+, OH+, O+, O++, H+) in coincidence with the projectile analyzed after the collision, i.e., either being H+, neutral H after single electron capture during the ionization event, or H- after double electron capture. After proper calibration we are thus able to determine a complete set of cross sections for the ionization of a molecular target by protons including the total and the partial cross sections and in addition also the direct ionization and the electron capture cross sections.     

A DC probe diagnostics for fast electron temperature measurements in tokamak edge plasmas

The tunnel probe is a new kind of Langmuir probe for use in the tokamak scrape-off layer. It provides simultaneous measurements of electron temperature and parallel ion current density with high frequency at the same point in space. We describe ongoing work to characterize the ion flows within the probe, and to calibrate the diagnostics using 2D kinetic simulations. Presented at 5th Workshop “Role of Electric Fields in Plasma Confinement and Exhaust”, Montreus, Seitzerland, June 23–24, 2002.     

Attosecond strobing of two-surface population dynamics in dissociating H2+

Using H2+ and D2+, we observe two-surface population dynamics by measuring the kinetic energy of the correlated ions that are created when H2+ (D2+) ionize in short (40-140 fs) and intense (10(14) W/cm2) infrared laser pulses. Experimentally, we find a modulation of the kinetic energy spectrum of the correlated fragments. The spectral progression arises from a hitherto unexpected spatial modulation on the excited state population, revealed by Coulomb explosion. By solving the two-level time-dependent Schr?dinger equation, we show that an interference between the net-two-photon and the one-photon transition creates localized electrons which subsequently ionize.     

Nonlinear model for coherent electric field structures in the magnetosphere

A new pseudo-three-dimensional electron hole in a magnetized plasma is possible when the low-frequency ion dynamics is taken into account. The newly found nonlinear Bernstein-Greene-Kruskal stationary solution, whose parallel phase velocity ranges between almost zero and the electron thermal speed, has the form of a cylinder that is tilted relative to the magnetic field. These structures are interpreted as three-dimensional electron holes coupled with hydrodynamic vortices, and provide a possible theoretical explanation for the POLAR and FAST satellite observations of coherent structures characterized by bipolar spikes of the parallel electric field and large perpendicular ion kinetic energies.     

新型金属锌有机膦酸盐的合成与光谱研究

通过水热法合成了Zn的两种新型有机膦酸盐,Zn(4,4’-bipy)(HBCP)1和[Zn2(phen)2(BCP)(H2BCP)].H2O2。其中化合物1为二维结构,Zn2+采用四面体配位方式,而化合物2为零维结构,Zn2+有五配位和六配位2种的配位方式。还利用了一维FTIR、热微扰下的二维IR相关光谱、Fluorescence和UV-VisDRS光谱等研究手段对化合物进行了研究,探讨了其结构与性能的关系,发现了化合物1以350nm激发,在412和520nm左右出现两个宽带发射峰,而化合物2在336nm激发下只在398nm处出现宽带发射峰。     

Coulomb explosion of large polyatomic molecules assisted by nonadiabatic charge localization

The electron-nuclear dynamics of the Coulomb explosion of a large polyatomic molecule, anthracene, is probed using kinetic energy distributions of produced H+ ions. The kinetic energy release of ejected protons exceeds 30 eV for anthracene exposed to 10(14) W cm(-2), 800 nm pulses of 60 fs duration. We propose a strong-field charge localization model, based on nonadiabatic dynamics of charge distribution in a (multiply) ionized molecule; the charge localization lasts many laser periods and is sustained through successive ionizations of the molecular ion. The model explains quantitatively the dependence of the H+ kinetic energy on the laser intensity. Dissociative ionization of a polyatomic molecule enabled by long-lived charge localization is a new type of electron-nuclear dynamics and is essential for understanding the pathways of molecular or ionic fragmentation in strong fields.     

Investigation of electron localization in harmonic emission from asymmetric molecular ion

We theoretically investigate the electron localization around two nuclei in harmonic emission from asymmetric molecular ion. The results show that the ionization process of electron localized around one nucleus competes with its transfer process to the other nucleus. By increasing the initial vibrational level, more electrons localized around the nucleus D+tend to transfer to the nucleus He2+so that the ionizations of electrons localized around the nucleus He2+increase. In this case, the difference in harmonic efficiency between He H2+and He D2+decreases while the difference in harmonic spectral structure increases. The evident minimum can be observed in the harmonic spectrum of He H2+compared with that in the spectral structure of He D2+, which is due to the strong interference of multiple recombination channels originating from two nuclei. Time-dependent nuclear probability density, electron-nuclear probability density, double-well model, and time-frequency maps are presented to explain the underlying mechanisms.     

Density functional theory study on ion adsorption and electroosmotic flow in a membrane with charged cylindrical pores†

ABSTRACT

Ion adsorption and electroosmotic flow induced by an external electric field have a variety of practical applications, especially for membrane technology. In this work, a partially perturbative density functional theory (DFT) based on the modified fundamental measure theory was applied to investigate the ion density distributions and partitions in a charged cylindrical pore. Different types of electrolyte solutions, including both charge symmetric and asymmetric, were examined using the proposed theory with various pore diameters, bulk densities, ion valencies and surface charge densities. The ion concentration profiles calculated with the theory exhibit good agreements with the results of the Monte Carlo simulations, while the results of the Poisson–Boltzmann equation deviate greatly especially for the high valence electrolytes in narrow cylindrical pores. Some interesting phenomena discovered in both experiments and simulations, such as the reverse distribution of the ions and charge inversion, can be well reproduced with the DFT. Based on the ion concentration distributions obtained from the DFT, the transient velocity profiles of the electroosmotic flow in the charged cylindrical nanopores were calculated with the Navier–Stokes (NS) equation. The characteristics of the electroosmotic flow were discussed under the different bulk electrolyte concentrations and thickness of the electric double layer inside the nanopore. The enhancement of the velocity near the pore wall, which cannot be described by the traditional theory, was well characterised by the DFT combined with the NS equation.     

四氟化碳分子电离解离过程中的异构化动力学

采用离子动量成像谱仪研究了能量为1.0 ke V的电子束碰撞条件下CF₄分子的解离动力学.实验上,对解离离子的三维动量进行了成像测量,通过离子飞行时间关联谱识别了CF₄²⁺异构化生成F₂⁺分子的两个通道:F₂⁺+CF₂⁺与CF⁺+F₂⁺+F,得到了两个通道的离子动能及动能释放分布.对于其中的三体解离通道,我们进一步采用Dalitz图与Newton图等三体动力学分析方法对解离碎片的动量关联进行了分析.该通道以两个带电离子的背对背出射为主,中性的F原子作为旁观者只得到极小的反冲动量.