稀有气体原子注入缺陷性纳米碳管的分子动力学模拟

采用TLHT势和经典分子动力学方法研究了稀有气体原子(He，Ne，Ar，Kr，Xe)进入带缺陷的单壁纳米碳管(SWCNT)的动力学过程，计算出了稀有气体原子分别从管壁和管口入射时，它们能封装在SWCNT中的能量阈值E_k0，并与理想结构情形做了比较.结果表明：随着管壁缺陷半径r的增加，E_k0减小；当r<4.5 ?时，给定合适的初始动能，稀有气体原子能封装在纳米碳管中；而r=4.5 ?时，稀有气体原子不能封装在碳管中，且此时缺陷对Ar，Kr和Xe的输运特性有很大影响. 关键词： 纳米碳管 缺陷 稀有气体原子 分子动力学模拟     

He,Ne,Ar,Kr和Xe原子电子的动量密度分布研究

对He,Ne,Ar,Kr和Xe原子体系中电子在动量空间的性质进行了系统的理论计算研究.采用自洽场HFR方法计算了坐标空间He,Ne,Kr和Xe原子体系单电子径向波函数,动量空间的单电子波函数由坐标空间原子体系单电子径向波函数通过运用傅立叶变换计算得到.在冲量近似条件下,进一步计算研究了这些原子的单电子动量密度分布和原子体系总的Compton轮廓.计算结果与已有的实验实验值和其他文献的理论计算结果比较表明,本文计算的结果是准确的.     

用模型势方法研究正电子与稀有气体的弹性散射

用模型势方法和STO波函数系统地计算了低能正电子与He, Ne, Ar, Kr, Xe和Rn惰性气体原子在非弹性阈值以下的散射角分布, 计算结果与已有的理论和实验数据吻合. 通过对算得的大量微分截面(散射角从20°到160°)的数据进行分析, 总结出了低能正电子与惰性气体原子弹性散射的规律.     

三原子准分子Kr_2F激光的实验研究

本文报道电子束泵浦的三原子稀有气体卤化物准分子Kr_2F激光的一些实验结果.观测了混合气体Ar(或者Ne,Kr,He)/Kr/NF_3(或者F_2)/N_2在不同混合比例时的激光运转情况.还进而研究了气体温度对激光发射特性的影响.     

电荷剥离截面的计算

采用二体碰撞近似(BEA)和托马斯费密近似(TFA),计算了多电荷离子(3Li2+,6C5+,10Ne+,18Ar+,36Kr+,54Xe+)的势函数分布和电子动量分布,以及它与中性原子H和He碰撞的电荷剥离截面. 关键词：     

稀有气体原子在纳米碳管中的周期性振荡

采用TLHT势和经典分子动力学方法研究了稀有气体原子进入单壁纳米碳管(SWCNT)的动力学过程，计算得出SWCNT能吸入稀有气体原子(He，Ne，Ar，Kr，Xe)的管径阈值r₀分别为6.3 ?，7.0 ?，8.6 ?，8.6 ?，8.6 ?，同时计算了对应的每种稀有气体原子能封装在不同管径的SWCNT中的最大初始动能E_k0.计算给出有趣的结果是封装在纳米碳管中的稀有气体原子在管中不停地作周期性振荡，振荡周期与原子进入管中的能量无关，振幅与原子进入管中的能量有关，即振幅随着入射能量的增加而增加.分析表明：给定合适类型的碳管，具有很小初始动能的稀有气体原子可在碳管中稳定的周期性振荡，其振荡频率可达GHz.     

惰性气体黏度的剩余熵标度模型

黏度是能源、动力、化工等系统设计分析中常用的重要物性参数.本文探讨了5种惰性气体(He、Ne、Ar、Kr、Xe)气相和超临界黏度的计算,以实际气体与同温度稀薄气体的黏度之比作为无量纲对比黏度,发现5种惰性气体的无量纲对比黏度与剩余熵之间满足同一单值函数关系,据此建立了惰性气体的气相和超临界黏度模型,其中稀薄气体黏度关联...     

SiH_4…Y(Y=He,Ne,Ar,Kr)体系中的分子间弱相互作用北大核心CSCD

在MP2/aug-cc-pvtz水平上对SiH4…Y(Y=He,Ne,Ar,Kr)复合物势能面上的4个构型进行优化,探讨了SiH4…Y(Y=Ar,Kr)复合物体系中的蓝移氢键结构和电子性质.含基组重叠误差(BSSE)校正的分子间相互作用能的相对大小可以判断复合物的相对稳定性递增顺序为:SiH4…He→SiH4…Ne→SiH4…Ar≈SiH4…Kr.且SiH4与Y(Y=He,Ne)体系之间的相互作用可归属为van der Waals力,而SiH4与Y(Y=Ar,Kr)之间的相互作用属弱氢键.NBO及电子行为分显示,SiH4…Y(Y=Ar,Kr)氢键复合物是一种非静电性质的弱氢键作用.另外,对各复合物中相关键鞍点处的电子密度拓扑性质分析也表明复合物中均存在非静电性质的分子间弱相互作用.     

SiH4…Y(Y=He,Ne,Ar,Kr)体系中的分子间弱相互作用

在MP2/aug-cc-pvtz水平上对SiH4…Y(Y=He,Ne,Ar,Kr)复合物势能面上的4个构型进行优化,探讨了SiH4…Y(Y=Ar,Kr)复合物体系中的蓝移氢键结构和电子性质.含基组重叠误差(BSSE)校正的分子间相互作用能的相对大小可以判断复合物的相对稳定性递增顺序为:SiH4…He→SiH4…Ne→SiH4 …Ar≈SiH4…Kr.且SiH4与Y(Y=He,Ne)体系之间的相互作用可归属为van der Waals力,而SiH4与Y(Y=Ar,Kr)之间的相互作用属弱氢键.NBO及电子行为分显示,SiH4…Y(Y=Ar,Kr)氢键复合物是一种非静电性质的弱氢键作用.另外,对各复合物中相关键鞍点处的电子密度拓扑性质分析也表明复合物中均存在非静电性质的分子间弱相互作用.     

SF6在惰性气体中输运性质的理论研究

利用Tang-Toennies势模型(以下简称TT势),计算了(Ne、Ar、Kr、Xe)-SF6相互作用势,在此基础上得到了SF6在惰性气体中的扩散系数,粘滞系数和热传导系数,通过相互作用势与M3SV势比较及输运性质与实验值的比较,说明了TT势模型是一种简单、可靠的势模型。     

Effect of long-range intermolecular forces on the drag of an oscillating disk and on the viscosity of gases

An experimental investigation has been made to determine the changes produced by ionization in the apparent viscosity of gases. The method used is that of the oscillating disk. In one series the gas was ionized by the gamma rays from an externally placed cesium-137 source. In the other two series of measurements the ionization was achieved with the aid of the alpha particles emitted from the surface of the oscillating disk coated with polonium 210.The measurements were made on nine gases at room temperature and in the pressure range of 1 mm Hg to 1.7 atm. The gases were: dry air, nitrogen, carbon dioxide, oxygen, helium, neon, argon, krypton and xenon. The experimental results showed that there is a very small change in the skin friction experienced by the disk.     

Gepulste UV-Strahlungsquelle zur Erzeugung eines hoch ionisierten Ausgangsplasmas niedriger Dichte

A 100 kV Z-pinch, pulse-filled with high-density xenon gas, is used as radiation source for photoionizing hydrogen or rare gases at filling pressures of 1–10 mtorr. This produces a homogeneous, magnetic field free, highly ionized (degree of ionization ≈10% in H₂ and ≈ 20% in Ar) plasma suitable for example, for collisionless shock wave experiments. Experimental and theoretical investigations have yielded information on the conversion of the stored electrical energy into radiation energy. As a result of fast magnetic compression and ohmic heating (the relatively low temperature of max. 6 eV due to multiple ionization of the xenon atoms being favourable) the xenon pinch absorbs 30% of the stored electrical energy. Investigation of the matching of the external circuit to theZ-pinch by means of the snowplow model shows that the energy transmission efficiency could be increased about 50% if the current half-cycle is made equal to the compression time. The suitability of the xenon pinch as a radiation source is due on the one hand, to the almost complete conversion of the absorbed energy into radiation and, in particular, to the spectral distribution of the radiation, which is favourable for the ionization of hydrogen. It is found that the radiation is mainly emitted in lines with maximum intensity at the same wavelength λ ≈ 700 Å as the maximum of the photoionization cross section owing to the low temperature of the xenon plasma.     

Free electron in compressed inert gases

The behavior of excess and intrinsic free electrons inside compressed inert gases is described as a function of pressure by using a pairwise approximation for the electron interaction with atomic surroundings. The change of sign from negative to positive for the xenon atom electric potential inside condensed xenon is predicted to occur at a pressure around 3 GPa, preventing slow electron embedding into solid xenon from the gas phase at higher pressure. To overcome this difficulty, the electrons should be injected into a solid sample just before its pulsed shock loading. The ionization of xenon by pressure and its further metallization are described by decreasing the forbidden gap at the expense of increasing the xenon ground electronic term and simultaneous splitting of the upper ionized electronic state. A good coincidence between the calculated and measured pressure of the dielectric-metal transition in xenon is demonstrated. The text was submitted by the authors in English.     

冲击压缩下甲烷-空气混合气体状态参数实验研究

 为研究强冲击状态下混入少量空气的甲烷气体的冲击状态参数,利用二级轻气炮加载技术,使加速到5 km/s的钨合金飞片撞击封装有常态下空气混入量依次为零（纯甲烷气体）、1%、5%、10%的甲烷-空气混合气体铝靶。采用六通道瞬态光学高温计记录冲击压缩气体的光辐射历程曲线,得到了相同初始条件下4种不同比例混合气体的冲击状态参数。结果表明,在强冲击压缩下,混合气体的冲击温度随着空气混入比例的增大而增高,冲击波后混合气体存在非平衡辐射过程。采用Saha电离平衡方程,对空气混入量为10%的混合气体的电离度进行了估算。结果表明,常态下空气含量C_air≤10%的甲烷 空气混合气体具有电探针保护能力。     

Observation of a transition in the dynamics of strong-field double ionization

The double ionization of argon and xenon in an intense laser field has been studied in detail using an electron-ion coincidence technique. The observed double ionization electron spectra in xenon show resonancelike structures here resolved for the first time. In argon, the featureless spectra are consistent with rescattering. This represents a clear transition in the dynamics of strong-field double ionization, analogous to the well-known transition between the tunneling and multiphoton regimes in single ionization.     

Investigation of a Hall MHD channel with an ionization-unstable plasma of inert gases

We investigate a promising scheme for using ionization-unstable plasmas of pure inert gases as the working medium for a magnetohydrodynamic (MHD) closed-cycle generator. Our experiments were carried out using a disc Hall MHD channel, with the flux of ionized gas created in a shock tube. Our working gas was xenon. In these experiments we measured the gas pressure, the flow velocity, the concentration and temperature of the electrons, the azimuthal current density, the distribution of potential in the channel, and the value of the near-electrode voltage drop. We recorded voltage-current characteristics for various values of magnetic field and load resistances. The results of these experiment showed that in an ionization-unstable plasma of inert gases without admixtures of alkali metal, the effective conductivity in the Hall channel increases significantly with increasing degree of criticality of the magnetic field, and the value of the maximum specific power extracted increases more rapidly than the specific power calculated by assuming “frozen” ionization. Zh. Tekh. Fiz. 67, 6–11 (December 1997)     

Local plasma parameters and integral characteristics of a magnetogasdynamic channel under conditions of ionization instability

Results are presented from an experimental investigation of the onset of ionization instability in a disk-shaped Faraday magnetogasdynamic channel attached to a shock tube. The experiments were carried out in a pure inert gas (xenon) without alkaline additives. A relation is found between the integral plasma characteristics of a nonequilibrium magnetogasdynamic channel and the local parameters of a plasma that is unstable against the ionization instability. Mechanisms for amplifying perturbations and increasing the effective conductivity are revealed. It is concluded that these effects stem mainly from the features of three-body recombination in rare gases.     

Magnetically-coupled piston pump for high-purity gas applications

Experiments based on noble elements such as gaseous or liquid argon or xenon utilize the ionization and scintillation properties of the target materials to detect radiation-induced recoils. A requirement for high light and charge yields is to reduce electronegative impurities well below the ppb (parts per billion, 1 ppb \(=1\times 10^{-9}\) mol/mol) level. To achieve this, the target material is continuously circulated in the gas phase through a purifier and returned to the detector. Additionally, the low backgrounds necessary dictate low-Rn-emanation rates from all components that contact the gas. Since commercial pumps often introduce electronegative impurities from lubricants on internal components or through small air leaks, and are not designed to meet the radiopurity requirements, custom-built pumps are an advantageous alternative. A new pump has been developed in Muenster in cooperation with the nEXO group at Stanford University and the nEXO/XENON group at Rensselaer Polytechnic Institute based on a magnetically-coupled piston in a hermetically sealed low-Rn-emanating vessel. This pump delivers high performance for noble gases, reaching more than 210 standard liters per minute (slpm) with argon and more than 170 slpm with xenon while maintaining a compression of up to 1.9 bar, demonstrating its capability for noble gas detectors and other applications requiring high standards of gas purity.     

Van der Waals molecules and collision pairs of noble-gas atoms ahead of a shock wave front

The effect of creation of an excess concentration of free electrons in an anomalously thick layer (≈5 cm) ahead of an explosively driven shock wave in noble gases is discussed and interpreted. This effect is the ionization of excited 1_u-state molecules produced due to the absorption of a small intensity flux (as compared to the ionization one) of photons (with energies substantially lower than the atom ionization threshold) by unexcited colliding complexes and van der Waals molecules. A model is proposed which explains the excitation of xenon molecules ahead of the radiationless shock wave of an open discharge. The absorption spectra of colliding complexes and van der Waals molecules adjacent to each other near the atomic absorption lines can be resolved into two spectra, and these spectra can be changed by an increase in gas temperature. As a result, radiation capable of exciting van der Waals molecules penetrates through the shock wave of an open discharge and excites xenon molecules there. The present work develops further the knowledge concerning the radiation energy transport in the shock wave front. It also proves that in front of an explosively driven shock wave a great number of excited molecules of noble gases are actually formed, and this means considerable progress toward a VUV laser with optical pumping. Translated from Preprint No. 56 of the P. N. Lebedev Physical Institute, Moscow, 1993.