Influence of multi-photon ionization of Xe on a XeF discharge induced by KrF laser irradiation

Excimer laser preionization induced by an external laser was investigated for XeF excimer laser discharge induced by a KrF laser, paying attention to the ionized species in the gas. Enhancement of amplified spontaneous emission (ASE) was observed for XeF gas discharge preionized by a KrF laser with and without its irradiation. In contrast, no ASE enhancement was observed for KrF gas discharge with KrF laser preionization. ASE enhancement was larger for the longer wavelength, which was close to the two-photon resonance of the Xe atom, when tunable KrF laser irradiation was used. These results indicate that multi-photon ionization of Xe atoms supplied the initial electrons to the laser-induced preionization.     

Gas density measurement of pulsed gas jets using XeF four-photon fluorescence induced by a KrF laser

The gas densities of two pulsed gas jets were measured together with spatial and temporal distributions by the XeF fluorescence induced by a KrF laser. The B-X and C-A transitions of XeF showed a biquadratic dependence on laser intensity when SF₆ was used as the F donor instead of F₂, and quadratic and cubic dependences on gas density, respectively.     

Experimental investigations of the formation of XeF*(B 2II1/2) excimer molecules during the injection of SF6 into a xenon plasma flow

The luminescence of XeF*(B ²II_1/2) molecules from a zone formed in the injection of SF₆ gas into a freely flowing xenon plasma jet is investigated. The experiments show that both the energy characteristics of the luminescence and the geometrical dimensions of the plasmachemical reaction zone can be controlled by varying the power input to the plasmatron and the mass flow rates of SF₆ and the xenon plasma. It is shown that the main contribution to the production of XeF*(B ²II_1/2) excimer molecules under the given experimental conditions is from two-particle ion-ion reactions involving Xe ions and SF ₆ ⁻ and SF ₅ ⁻ molecular ions. Zh. Tekh. Fiz. 68, 36–42 (February 1998)     

大气等离子体加工过程的原子发射光谱研究

大气等离子体加工反应过程中,等离子体发生装置的热稳定过程对去除率有直接影响,CF₄是化学反应中活性F*原子的提供者,O₂是重要的辅助气体。为了寻找这三者对大气等离子体加工反应过程的影响规律,采用大气等离子体加工系统进行加工、光谱仪监控等离子体反应过程的活性F*原子的光谱变化。实验结果表明,在大气压等离子体加工系统中: 热稳定后,活性F*原子强度基本不随时间变化;随着CF₄含量的增加,F*原子谱线轮廓发生了自吸收现象,这说明采用光谱法研究CF₄含量对活性F*原子含量的影响是不完全准确的;由于O₂易和CF₄解离的中间产物反应,抑制活性粒子重新组合,因此一定范围内随着O₂含量增加,活性F*原子增加。     

Analysis of the effect of foreign gases in the production of hyperpolarized 129Xe gas on a simple system working under atmospheric pressure

Experimental conditions that affect the degree of polarization of 129Xe gas were tested for a higher degree of polarization to facilitate a laboratory use of 129Xe NMR, primarily on the effect of addition of foreign gases. When He, N(2), or D(2) gas was added separately to pure Xe gas with natural isotope abundance, D(2) gas gave better results than the others in enhancing the degree of polarization in 129Xe atom. When these gases were added in mixture, however, N(2) plus He was proved to be more efficient than D(2) or He in enhancing the degree of polarization. As a result, the degree of polarization was found to be increased by more than an order, when diluent gases were properly mixed; polarization as high as 35% was reached at gas composition of 5% Xe, 10% N(2), and 85% He, whereas only a few percent was attainable when Xe gas was polarized without mixing any foreign gases [J. Magn. Reson. 150 (2), 156-160 (2001)]. These results were discussed on a basis of quenching and buffer effects of foreign gases. Polarization was also measured after separating the pure Xe gas from the mixture; value of 22% was obtained for the Xe gas isolated after solidification in liquid nitrogen trap. Build-up time of the polarization was also tested, which did not change remarkably depending on the gas composition.     

Temporal extension of stable glow discharges in fluorine-based excimer laser gas mixtures by the addition of xenon

The effect of addition of xenon on the long term homogeneity of discharges in F₂and ArF excimer laser gas mixtures was investigated in a small-volume discharge chamber. The gas mixture in the discharge chamber was preionized by X-rays. A special electrical excitation circuit containing a pulse forming line provided a long, square-shaped current pumping pulse of a predetermined duration to the discharge electrodes. The initiation and the development of the discharge was monitored via its fluorescence signal with an intensified CCD camera. We found that adding Xe up to partial pressures of 0.53 mbar extended the homogeneous phase of the discharge from 80 ns to approximately 200 ns in He/F₂as well as in He/Ar/F₂and Ne/Ar/F₂excimer laser gas mixtures. Monitoring of the ArF and XeF spontaneous emission signals showed that the formation of ArF excimers remained unaffected by the addition of xenon (up to 1.3 mbar) to the laser gas mixture.     

Gas-discharge XeF* (B→X) laser with high specific output energy

The discharge characteristics of the XeF* (BX) laser are investigated. The NF₃ and Xe partial pressure of the laser gas mixture and the total gas pressure have been varied. A highest specific output energy of 4.7 J/l with an efficiency of 0.5% was obtained from a X-ray preionized Ne/Xe/NF₃ gas mixture at 6 bar with single-pulse excitation through a multichannel spark gap.     

流动系统中的激光增强固体和液体129Xe核磁共振信号

在流动系统中,用半导体阵列激光器在低磁场下抽运Cs原子,由自旋交换碰撞产生极化的129Xe气体,在SY80M核磁共振谱仪中,冻成固体和液体后的极化度分别为216%和145%,和相同条件下未光泵的129Xe极化度相比,分别增强6000和5000倍.为将激光增强固体和液体129Xe用于量子计算提供了基础和可能.并对输运和相变过程中极化损失作了讨论 关键词： 光泵 激光极化 核磁共振信号 光和原子相互作用     

High-purity F atom beam source

Fluorine atoms are generated by 2.45 GHz microwave dissociation of 99.99% F₂ in a synthetic sapphire single-crystal discharge tube. Typical F₂ gas flow and beam intensity are: 0.1 mbar ls^?1 and 9.5×10¹⁷ atoms sterad^?1 s^?1. The measured degree of dissociation into atoms isD>98%. The high total F atom flux together with the purity of the beam seem to make the source a very promising device for both reaction kinetic-and molecular beam-experiments     

Hyperpolarized (131)Xe NMR spectroscopy

Hyperpolarized (hp) (131)Xe with up to 2.2% spin polarization (i.e., 5000-fold signal enhancement at 9.4 T) was obtained after separation from the rubidium vapor of the spin-exchange optical pumping (SEOP) process. The SEOP was applied for several minutes in a stopped-flow mode, and the fast, quadrupolar-driven T(1) relaxation of this spin I = 3/2 noble gas isotope required a rapid subsequent rubidium removal and swift transfer into the high magnetic field region for NMR detection. Because of the xenon density dependent (131)Xe quadrupolar relaxation in the gas phase, the SEOP polarization build-up exhibits an even more pronounced dependence on xenon partial pressure than that observed in (129)Xe SEOP. (131)Xe is the only stable noble gas isotope with a positive gyromagnetic ratio and shows therefore a different relative phase between hp signal and thermal signal compared to all other noble gases. The gas phase (131)Xe NMR spectrum displays a surface and magnetic field dependent quadrupolar splitting that was found to have additional gas pressure and gas composition dependence. The splitting was reduced by the presence of water vapor that presumably influences xenon-surface interactions. The hp (131)Xe spectrum shows differential line broadening, suggesting the presence of strong adsorption sites. Beyond hp (131)Xe NMR spectroscopy studies, a general equation for the high temperature, thermal spin polarization, P, for spin I ≥ 1/2 nuclei is presented.     

Reactive resonance in a polyatomic reaction

In the course of an extensive investigation aimed at understanding the detailed mechanisms of a prototypical polyatomic reaction, several remarkable observations were uncovered. To interpret these findings, we surmise the existence of a reactive resonance in this polyatomic reaction. The reaction of concern is F+CH4-->HF+CH3, and the abnormal attributes were revealed only near the reaction threshold. The discovery of reactive resonance in a polyatomic reaction is more than just an extension from a typical atom+diatom reaction. As shown here, it holds great promise to disentangle the elusive intramolecular vibrational dynamics of transient collision complex in the critical transition-state region.     

Theoretical study of the Ru + CH3F reaction

CASSCF-MRMP2 calculations have been performed to analyse the reaction of fluoromethane with a bare ruthenium atom. Potential energy curves emerging from the ground state and the first excited state of the reactants, Ru(⁵F, ³F;d⁷s¹) + CH₃F, were calculated for representative electronic states associated with different approaching modes of the fragments. Whereas no favourable channels correlating with the ground state asymptote were detected for the insertion of the ruthenium atom into the C–H bond of the methyl fluoride molecule, the oxidative addition of the C–F bond of this molecule to the metal atom along the reaction path evolving from the ground state of the fragments leads to the stable inserted product CH₃–Ru–F. Although forming less stable products, insertion of ruthenium into the C–H and C–F bonds of the fluorocarbon molecule can occur through electronic states which emerge from the excited triplet state asymptote.     

Long pulse electron beam excited XeF laser

Long pulse operation of the XeF laser has been achieved with a short gain length and medium intensity electron beam excitation for both Ar/Xe/NF₃ and Ne/Xe/NF₃ mixtures. Use of Ne as diluant strongly lower the threshold for lasing and give an important increase in extracted power. For a total mixture pressure of 2 atm about 6 mJ of 3500 Å radiation was obtained in a 400 ns fwhm pulse limited only by e-beam pulse length.     

Inert gas clusters ejected from bursting bubbles during sputtering

Ar(+)(n) cluster ions (n相似文献   

Observation of resonance condensation of fermionic atom pairs

We have observed condensation of fermionic atom pairs in the BCS-BEC crossover regime. A trapped gas of fermionic 40K atoms is evaporatively cooled to quantum degeneracy and then a magnetic-field Feshbach resonance is used to control the atom-atom interactions. The location of this resonance is precisely determined from low-density measurements of molecule dissociation. In order to search for condensation on either side of the resonance, we introduce a technique that pairwise projects fermionic atoms onto molecules; this enables us to measure the momentum distribution of fermionic atom pairs. The transition to condensation of fermionic atom pairs is mapped out as a function of the initial atom gas temperature T compared to the Fermi temperature T(F) for magnetic-field detunings on both the BCS and BEC sides of the resonance.     

A comparative study on the gas‐phase and liquid‐phase thermal isomerization reaction of α‐pinene

In this paper, a method of preparation of ocimene is investigated, which is obtained from isomerization reaction of α‐pinene. Two kinds of experimental apparatus are established for the investigation of the thermal isomerization reaction of α‐pinene. The behavior of thermal isomerization reaction of α‐pinene is respectively discussed in the gas phase and in the liquid phase. Under gas phase conditions, the conversion of α‐pinene is 80% and the selectivity of ocimene is 30%–33%. Under liquid phase conditions, the conversion of α‐pinene is 60% and the selectivity of ocimene is 50%–54%. According to the kinetic‐molecular theory of ideal gases, two kinds of reaction models are proposed to visualize the reaction process. In addition, the mechanism and kinetics of thermal isomerization reaction of α‐pinene are respectively discussed. The conclusion is that the gas phase reaction temperature is calculated to be 390–450 °C and the liquid phase reaction temperature is calculated to be 450–550 °C. From a bond dissociation energy point of view, results support the hypothesis that the reaction involves biradical intermediates. Copyright © 2012 John Wiley & Sons, Ltd.     

l mixing and dissociation of Rydberg molecules accompanying slow collisions with inert-gas atoms

Processes involving a change of orbital angular momentum l and the dissociation of Rydberg molecules when they collide with inert-gas atoms are considered, using a method based on analyzing the terms of the interacting systems. The proposed method makes it possible to take into account the perturbations in a large group of Rydberg states that weakly penetrate into the ion core and to go beyond the limits of the two-level approximations [R. F. Stebbings and F. B. Dunning, eds., Rydberg States of Atoms and Molecules (Cambridge University Press, Cambridge, 1983; Mir, Moscow, 1985)] widely used in the theory of l mixing with the participation of Rydberg atoms. Using the Na**(nd)+Xe reaction as an example, it is demonstrated that this method gives good results in a wide range of variation of the principal quantum number n of the Rydberg electron (n≈10–40). Features of the l mixing and dissociation of Rydberg molecules are studied for the H₂**+Xe system. It is shown that collisional dissociation occurs by the formation of an intermediate Rydberg state of the molecules, followed by self-decay into a dissociative continuum. Zh. éksp. Teor. Fiz. 114, 100–113 (July 1998)     

Excimer ArF/XeF lasers providing high-power stimulated radiation in Ar/Xe and F lines

Lasing in atomic lines of noble gases and fluorine, prior to excimer radiation, was observed in an electric discharge ArF/XeF excimer laser. Some Ar/Xe lines end at metastable levels, which are very important for the formation of ArF/XeF excimer molecules. Five new lasing lines of atomic fluorine have been obtained. Consideration is given to the use of lasing in atomic and molecular lines, that occurs in one burst, in investigations of the excitation kinetics of excimer states under the conditions of a high-pressure electric discharge.