The nature and properties of a plasma

We have good reason to believe that much if not most of the matter in the universe is in the plasma state. This state can be described by comparing it with that of an ordinary gas, which is familiar to all of us, where large numbers of molecules move in all directions with different velocities along criss-cross paths, each sudden change of direction of movement being caused by a collision between two or more particles. But whereas in a gas all particles are electrically neutral, in a plasma charged fragments of formerly neutral molecules, positive and sometimes negative ions and electrons, take part in the random motion together with their neutral companions as well as with light quanta (von Engel 1955). In the gas of many stars, the sun, and certain apparatus in our terrestrial laboratories, charged particles predominate over neutral particles; these conditions approach a state called the fully ionized plasma (Spitzer 1956).     

Single-Walled Carbon Nanotubes Acting as Controllable Transport Channels

The motion and equilibrium distribution of water molecules adsorbed inside neutral and negatively charged singlewalled carbon nanotubes (SWNTs) have been studied using molecular dynamics simulations (MDSs) at room temperature based on CHARMM (Chemistry at HARvard Molecular Mechanics) potential parameters. We find that water molecules have a conspicuous electropism phenomenon and regular tubule patterns inside and outside the charged tube wall. The analyses of the motion behaviour of water molecules in the radial and axial directions show that by charging the SWNT, the adsorption efficiency is greatly enhanced, and the electric field produced by the charged SWNTs prevents water molecules from flowing out of the nanotube. However, water molecules can travel through the neutral SWNT in a fluctuating manner. This indicates that by electrically charging and uncharging the SWNTs, one can control the adsorption and transport behaviour of polar molecules in SWNTs for using as a stable storage medium or long transport channels. The transport velocity can be tailored by changing the charge on the SWNTs, which may have a further application as modulatable transport channels.     

Neutral gas free molecular flow algorithm including ionization and walls for use in plasma simulations

Several plasma devices, including Hall and ion thrusters, operate by ionizing a low density neutral gas for which the mean free path between collisions of gas molecules is greater than typical device dimensions. In general, the discrete-particle algorithms used to calculate the neutral gas ignore velocity changes due to collisions between gas molecules. However, particle algorithms are a source of unphysical statistical noise that may detract from the study of the plasma physics, the prime purpose of most simulations. In this paper we present a new neutral gas algorithm for use in plasma simulation codes that exploits the fact that very few collisions change the velocity of neutral gas molecules. The algorithm assumes that the particle velocity distribution function for neutrals emitted from a given surface remains unchanged except for a scale factor that reflects the loss of neutrals to ionization. The sources of neutrals may be gas inlets, and isotropic, thermally accommodated, gas molecules coming off chamber surfaces including recombined ions. The algorithm is implemented in two dimensions (R–Z) with emitting surfaces represented as surfaces of revolution. The advantage of this algorithm over the conventional particle approach is the absence of statistical noise.     

Trapping neutral molecules in a traveling potential well

A series of pulsed electric fields can be arranged such that it creates a traveling potential well in which neutral dipolar molecules can be confined. This provides a method to transport, to decelerate, and to cool a sample of neutral molecules while maintaining the initial phase-space density. This method is described using the concept of phase stability. The oscillating motion of molecules in the traveling potential well, reaching a minimum velocity spread corresponding to a translational temperature of 4 mK, is experimentally observed.     

Using molecules to measure nuclear spin-dependent parity violation

Nuclear spin-dependent parity violation arises from weak interactions between electrons and nucleons and from nuclear anapole moments. We outline a method to measure such effects, using a Stark-interference technique to determine the mixing between opposite-parity rotational/hyperfine levels of ground-state molecules. The technique is applicable to nuclei over a wide range of atomic number, in diatomic species that are theoretically tractable for interpretation. This should provide data on anapole moments of many nuclei and on previously unmeasured neutral weak couplings.     

Strong-field induced vibrational coherence in the ground electronic state of hot I2

We observe large amplitude coherent vibrations in vibrationally hot ground state neutral I2 molecules created through "Lochfrass," or "R-selective ionization." We directly measure the phase and amplitude of the vibrations. Our results support the notion of enhanced ionization at large internuclear separation over recent theoretical predictions for heavy molecules. Furthermore, simulations of the vibrational motion show that for Lochfrass the vibrational coherence, contrary to most coherent control schemes, is stronger for hot molecules than for cold molecules.     

Population inversion in fluorescing fragments of super-excited molecules inside an air filament

An original idea is reviewed.When a molecule is pumped into a super-excited state,one of its decay channels is neutral dissociation.One or more of the neutral fragments will fluoresce.Hence,if a lower state of such fluorescing fragments was populated through other channels but with a lower probability,population inversion of the fluorescing fragments would be naturally realized.This idea seems to be validated,so far,by comparing published work on three hydrocarbon molecules,CH4,C2H2,C2H4,and water vapor,H2O.After super-excitation in a femtosecond laser filament in air mixed with these molecules,the fluorescence from the CH or OH fragments exhibits population inversion,i.e.,amplified spontaneous emission was observed in the backscattering direction of the filament.     

铁小檗碱化合物结构的密度泛函理论研究

本工作采用密度泛函理论(B3LYP)方法对铁小檗碱化合物的中性分子及离子进行了结构优化和频率计算.结果表明:无论是中性分子还是离子,铁小檗碱物化合物基态结构都是小檗碱基态结构中的与N原子相邻的C10原子上键合一个Fe原子形成的.其阳离子结构具有C_1对称性和~3A电子态;中性分子的基态结构具有C_1对称性和2A电子态;阴离子的基态结构具有C1对称性和5A电子态.当铁小檗碱物化合物的阳离子得到一个电子后,C(10)-Fe(26)及Fe(26)-H(44)的键长都有所变短;当中性分子得到一个电子变成阴离子后,C(10)-Fe(26)及Fe(26)-H(44)的键长都有所增加.     

铁小檗碱化合物结构的密度泛函理论研究

本工作采用密度泛函理论（B3LYP） 方法对铁小檗碱化合物的中性分子及离子进行了结构优化和频率计算。结果表明:无论是中性分子还是离子,铁小檗碱物化合物基态结构都是小檗碱基态结构中的与N原子相邻的C10原子上键合一个Fe原子形成的。其阳离子结构具有C1对称性和3A电子态;中性分子的基态结构具有C1对称性和2A电子态;阴离子的基态结构具有C1对称性和5A电子态。当铁小檗碱物化合物的阳离子得到一个电子后,C(10)-Fe(26)及Fe(26)-H(44)的键长都有所变短;当中性分子得到一个电子变成阴离子后,C(10)-Fe(26)及Fe(26)-H(44)的键长都有所增加。     

Neutralization of mass-selected cluster ions by charge transfer reactions

Mass-separated beams of clusters with a single, well-defined number of atoms or molecules are indispensable for studies of cluster properties. This paper presents a technique with the potential to generate such a beam which contains neutral clusters of one size only. For this purpose mass-selected cluster ions have been neutralized by charge transfer reactions in metal and sulphur vapors. Relative charge exchange cross sections were measured for different cluster sizes. They reveal pronounced variations of the electronic structure of these particles. Thus, the study of charge transfer processes is introduced as a method to probe the positions of electronic energy levels in neutral clusters.     

Longitudinal focusing and cooling of a molecular beam

A neutral polar molecule experiences a force in an inhomogeneous electric field. This electric field can be designed such that a beam of polar molecules is exposed to a harmonic potential in the forward direction. In this potential the longitudinal phase-space distribution of the ensemble of molecules is rotated uniformly. This property is used to longitudinally focus a pulsed beam of ammonia molecules and to produce a beam with a longitudinal velocity spread of 0.76 m/s, corresponding to a temperature of 250 mu K.     

Associative electron stimulated desorption of neutral CO molecules

The Electron Stimulated Desorption (ESD) of neutral CO molecules was studied on polycrystalline Ni surface. Combined ESD and temperature programmed desorption (TPD) measurements were used to observe the variations of neutral ESD yield in dependence on CO coverage, containing direct information about the cross section for ESD of neutral CO molecules in relation to various CO adsorption states. The results show evidence of ESD of neutral CO molecules from dissociative adsorption states. The cross section for this associative ESD process is relatively high in comparison with the CO ESD cross section for molecular CO adsorption. This work was supported by the Czech Grant Agency under the Grant No. 202/99/1714 and by the Czech Ministry of Education, Youth and Sports under the Project No. VS97116.     

荧光法研究几种分子在海藻酸钙空心胶囊中的缓释性能

实验中选取了带有正电罗丹明6G分子、带有负电荷荧光素分子、中性的尼罗红分子和生物分子R-藻红蛋白为模型分子.将这几种分子分别包封于海藻酸钙窄心胶囊中.实验表明囊芯分子的电性对其在海藻酸钙空心胶囊中缓释性能有影响,带有正电荷罗丹明6G分子的扩散过程中,多孔聚合物骨架扩散是主要过程.中性分子则表现出来一个膜相溶出和多孔聚合物骨架扩散共同控制的过程.带有负电荷荧光素分子,由于静电排斥作用,加剧囊芯分子的运动.从而使得荧光素分子可以直接从膜相溶出.此外.南于胶囊囊壁上带有负电,不论是带有正电荷还足带有负电荷的分子都会延长其达到扩散平衡的时间.而电中性分子由于没有库仑相互作用的影响更容易达到平衡.囊芯和囊辟相互作用强的其扩散系数小,反之其扩散系数大.R-藻红蛋白的扩散完全是一个多孔聚合物骨架扩散控制的过程.由于分子的体积比较大,因此扩散的平衡时间也比较长.     

高功率微波有效电场强度对大气折射率的影响

 高功率微波的强电场与大气作用使空气电离，中性分子的电离频率与等效电场强度、大气压强密切相关。在一个较宽的范围内研究电子与大气中性分子的相互作用，分析讨论了高功率微波传输一个脉冲后电子浓度和折射率随微波有效电场强度的变化。     

Modeling process of the neutral beam re-ionization loss

The basic process of re-ionization loss was studied. In the drift duct there are three processes leading to re-ionization loss: the collision of neutral beam particles with the molecules of background gas, similar collisions with released molecules from the inner wall of the drift duct and the ferret-collisions among particles with different energy of the neutral beam. Mathematical models have been developed and taking EAST-NBI parameters as an example, the re-ionization loss was obtained within these models. The result indicated that in the early stage of the neutral beam injector operation the released gas was quite abundant. The amount of re-ionization loss owing to the released gas can be as high as 60%. In the case of a long-time operation of the neutral beam injector, the total re-ionization loss decreases from 13.7% to 5.7%. Then the re-ionization loss originating mainly from the collisions between particles of the neutral beam and the background molecules is dominant, covering about 92% of the total re-ionization loss. The drift duct pressure was the decisive factor for neutral beam re-ionization loss.     

六参数高精度双原子分子解析势能函数

提出一种构造解析势能函数的新方法,得到一种六参数解析势能函数,该势能函数适用于多种基本类型的双原子分子.用同核中性基态双原子分子Li₂-X¹Σ_g⁺、Na₂-X¹Σ_g⁺,异核带电基态双原子分子离子(BC)^--X³∏,异核中性激发态双原子分子PbS-A¹Σ⁺、BaO-A¹Σ,异核带电激发态双原子分子离子(CS)⁺-A²∏,同核中性激发态双原子分子K₂-B¹∏_u,同核带电激发态双原子分子离子N₂⁺-B²Σ_u⁺等共36个算例对该势能函数进行验证,计算结果与RKR(Rydberg-Klein-Rees)数据或振动能谱实验数据高精度符合.同时发现,在分子振动能谱计算精度方面,该势能函数总体上优于Murrell-Sorbie势能函数.     

Rydberg excitation of neutral nitric oxide molecules in strong UV and near-IR laser fields

Rydberg state excitations of neutral nitric oxide molecules are studied in strong ultraviolet(UV) and near-infra-red(IR) laser fields using a linear time-of-flight(TOF) mass spectrometer with the pulsed electronic field ionization method.The yield of Rydberg molecules is measured as a function of laser intensity and ellipticity,and the results in UV laser fields are compared with those in near-IR laser fields.The present study provides the first experimental evidence of neutral Rydberg molecules surviving in a strong laser field.The results indicate that a rescattering-after-tunneling process is the main contribution to the formation of Rydberg molecules in strong near-IR laser fields,while multi-photon excitation may play an important role in the strong UV laser fields.     

Optical fractionation of an ensemble of impurity molecules over the magnitude of a Stark moment induced by an amorphous matrix

A method of selective (with respect to the Stark effect) burning of a spectral hole in the 0-0 absorption band of zero-dipole impurity molecules is suggested. It is shown that in combination with the Stark modulation of the optical density of a sample, this method makes it possible to determine that contribution to the total absorption and luminescence of the sample that the impurity molecules with a preset magnitude of the matrix-induced Stark moment (provided this magnitude exceeds the mean value for the entire ensemble) make. This allows one to experimentally study both the distribution of impurity molecules over the magnitude of the Stark moment and the correlation of the Stark moment with other parameters of impurity molecules.     

Chemical physics of the upper atmosphere

Modern concepts of the structure of the ionosphere and dynamics of its perturbations related to geomagnetic and solar activity perturbations are considered. It is shown that communication and navigation satellite systems depend substantially on the state of the ionosphere. The role played by Rydberg atoms and molecules of neutral ionospheric plasma components excited in collisions with electrons in the formation of microwave radiation of the upper atmosphere is discussed. A new physical mechanism of the delay of satellite signals cased by a cascade of reemissions from Rydberg states over the decimeter range is suggested.