Biography

The mononegative, dinegative and monopositive ions of biphenylene have been formed in solution. The electronic spectra of the negative ions (in tetrahydrofurane and dimethoxyethane solution) have been measured in the range 10 000–44 000 cm^-1, and that of the positive ion (in H₂SO₄ solution) in the range 10 000–35 000 cm^-1. The presence of paramagnetic ions in the solutions of the singly-charged species has been confirmed by measurement of electron spin resonance absorption. The long wavelength electronic spectra of the monopositive and mononegative ions are closely similar, which confirms the essentially ‘aromatic’ character of the biphenylene structure. Assignments are proposed for the principal bands in the spectra of the ions and the neutral molecule. Explicit calculation of the energies of the excited states by an approximate self-consistent field molecular orbital method yields results in reasonably good overall agreement with the experimental energy spectra. There is evidence from relative intensities of some of the bands that the ‘pairing’ of bonding and antibonding sets of molecular orbitals which is characteristic of benzenoid alternant hydrocarbons is partially removed in biphenylene. This may result from a difference of electronegativity of the carbon atoms in the 4-membered ring from that of the remaining carbon atoms.     

The polarization of light emitted from sputtered Mg atoms

The polarization fraction of light emitted from Mg atoms excited during bombardment of the Mg polycrystalline target by low-energy Ne⁺ ions has been measured. Taking into account the results, a possible mechanism of excitation of sputtered atoms is suggested.     

单、双电荷离子与原子碰撞中的激发态和发射截面比较

本文给出了单、双电荷离子和He,Ne,Ar,碰撞过程中产生的激发态的实验结果。He^q+,Ar^q+(q=1,2)离子束实验室能量为(70—170)×q keV。光学测量由光学多道分析系统(OMA)完成,波长范围为200—800nm。观察到单、双电荷离子和原子碰撞中各种不同的激发过程,讨论了发射截面和入射离子电荷数、势能亏损的依赖关系。 关键词：     

Ion-energy distributions in liquid-metal-ion sources

Energy distributions of mass-separated ions emitted from liquid-metal-ion sources using Ni-B-Si and Pt-P-Sb alloys have been measured in a dynamic range of four orders of magnitude. Low-energy tails are observed on the energy-per-unit ion charge for singly-charged ions, in contrast with doubly-charged ions. The higher ion-emission current brings about longer tails. Rather flat tails are also observed on the high-energy side for M⁺ ion species in the Pt-P-Sb alloy LMIS, where the M²⁺ intensity is larger than the M⁺ one. The origins of these energy tails are discussed.     

On the excitation mechanism of the He-Ar hollow cathode laser

Investigations were carried out on the Ar-II 476.5 nm laser to obtain information on possible excitation mechanisms. The He-Ar hollow cathode discharge was excited by square wave current pulses. From the results of measurements it could be concluded that collisions of the second kind between He 2³ S metastable atoms and ground state Ar ions are dominant in the excitation of the upper laser level. This is also supported by results obtained in the case of the He-Kr hollow cathode laser, where the upper level of the Kr-II 469.4 nm laser is excited by a similar collision process.     

The formation of excited states of sputtered yttrium atoms

Optical spectra of ion-photon emission of atoms sputtered by bombarding the yttrium target surface with 40-keV Xe⁺ ions are studied experimentally. It is found that the levels corresponding to transitions from the 4d shell are excited more efficiently in the sputtering process. Possible new mechanisms for the excitation of atomic levels in the sputtering of a solid are considered.     

Isotope shift calculations for open-shell atoms and ions: an extension to the RATIP program

During the past decade, the Ratip program has been found useful for calculating a variety of atomic properties, including energies, transition probabilities, Auger parameters as well as a number of excitation, ionization and capture cross sections for processes with a single electron in the continuum. Recently, in addition, this suite of programs was extended to predict also the isotope shift and hyperfine parameters of open-shell atoms and ions. Here, we review the latest developments of the Ratip program with emphasis on the specific mass-shift M ^sms and field-shift F parameters. Detailed computations for these parameters have been carried out especially for the $4s\;^2S_{1/2} - 4p\;^2P_{1/2,3/2}$ transitions at ~ 397 nm of singly-charged Ca^?+? ions and are compared with available data from the literature.     

Energy spectrum of field ionization at a single atomic site

Energy deficit spectra of field ions coming from above a single atomic site are measured by using an atom-probe FIM modified with a Möllenstedt energy analyzer. This device offers a resolution of 5 × 10^?5 and is inherently more efficient and less noisy than a retarder. The energy spectra made up of 10 to 100 ions/sec are displayed on the screen of an assembly of two microchannel plates and are photographically recorded within a few seconds. Jason peaks for H₂⁺ and Ne⁺ are confirmed, and are also found for He⁺. High-order multiple peaks appear when ions are taken from the flat, closely packed net planes of W and Ir field ion emitters. The results are in quantitative agreement with a resonance model similar to one by Alferieff and Duke and by Jason. Noble gas ions are also observed from the forbidden zone near the surface, and interpreted as apex-adsorbed atoms ionized by or after excitation by the electron shower coming from farther-out field ionization of other gas atoms. Energy from excited metastable apex-adsorbed atoms may account for artifact vacancies observed particularly when field evaporation is performed in neon.     

高电荷态离子N6+与He原子碰撞激发过程的实验研究

利用电子迴旋共振(ECR)多电荷离子源产生的高电荷态离子束和LHT-30VUV真空紫外单色仪,对N⁶⁺与He碰撞激发过程进行研究,观察到三种碰撞激发过程:(1)单电子俘获;(2)双电子俘获;(3)入射离子直接激发过程。 关键词：     

On the velocity distribution of excited Fe-atoms by sputtering of iron

From the velocity distribution of excited sputtered particles detailed information on the excitation process can be obtained. In the present paper the first direct measurement of velocity distribution of excited atoms sputtered from a metal target is presented. The irradiation of the Fe-target was performed with 10keV Ar⁺-ions. The sputtered atoms were detected using pulsed laser induced fluorescence (LIF). The sputtered Fe atoms in the metastable statea ⁵ F ₅ at 0.86 eV shows a much broader distribution, than found for the ground-state atoms, but no energy threshold, implied in the statistical excitation models, was found.     

Nonradiative transition to the ground state and superelastic scattering of exited atoms upon impact on the surface of wide-bandgap dielectrics

The impact of excited cesium atoms on sapphire and glass surfaces have been experimentally studied. It is established that the probability of electron excitation quenching upon impact of an atom on the dielectric surface is close to unity. The velocity distribution of unexcited atoms upon scattering from the surface has been determined using the time-of-flight technique. The kinetic energies of most of these atoms are several tens of times greater than the energy of thermal motion of the excited atoms impinging on the surface. Conversion of the internal energy of atoms into their kinetic energy is explained in terms of nonradiative electron transitions with simultaneous excitation of lattice vibrations in the dielectric crystal. This mechanism of atomic excitation quenching near the dielectric surface explains the significant difference between the energies of atoms upon superelastic scattering and upon photodesorption from an adsorbed state.     

Narrow 3-photon autoionizing resonances in Tl and Yb

Narrow autoionizing resonances have been observed in Yb and Tl using direct 3-photon excitation of ground state atoms. The linewidth is 0.9 cm^-1 in Yb and 0.4 cm^-1 in Tl. Autoionizing levels in both atoms correspond to doubly excited electronic states. This is the first observation of such states in Tl.     

Preparation and characterization of tunable YVO4: Bi, Sm phosphors

Yttrium vanadate phosphors co-doped with Bi³⁺- and Sm³⁺ ions have been prepared via the solid-state reaction as well as via the sol-gel method. The luminescence studies demonstrate the potential of the prepared phosphors as multi-color emitters, which can be achieved by adjusting the excitation wavelengths. The excitation spectra of Bi³⁺- and Sm³⁺ co-doped phosphors clearly revealed energy transfer from Bi³⁺ to Sm³⁺ ions. When the co-doped phosphors were excited at 254 nm, the emission from Bi³⁺ was dominant. Upon excitation at 365 nm, the emission from both Bi³⁺ and Sm³⁺ was detected. With 410 nm excitation, Sm³⁺ ions were selectively excited to yield intense red emission. It is shown that the prepared phosphors with optimal concentrations of Bi³⁺ and Sm³⁺ can be excited at 254, 365 and 410 nm to yield yellow, orange and red emissions, respectively.     

Electron-impact excitation of the 3 P o and 3 D o levels of a nickel atom

The excitation cross sections of transitions from the ³ P ^o and ³ D ^o levels of a nickel atom in electron-atom collisions at an exciting-electron energy of 50 eV have been analyzed by the method of extended crossing beams with detection of the optical signal from excited atoms. Eleven optical excitation functions have been recorded in the electron-energy range of 0?C200 eV. The direct excitation cross sections of the energy levels and the contribution of the cascade transitions were calculated using the data obtained.     

Migration of excitation in transfer of spectral-line radiation

A simple mathematical model is developed for the transfer of energy through a gas by the combined effect of radiative transfer and migration of excitation. The “excitation” is carried through the gas by a succession of atoms which experience resonant excitation exchange; it thus appears to random walk through the medium. The theory developed here is valid when the distance traveled by an atom while excited is much larger than the typical distance at which two atoms can exchange excitation (roughly 10^-6cm). The model is expressed in terms of a pair of coupled transport equations for the intensity of radiation and the density of excited atoms, which are solved by means of a generalized discrete-ordinate technique. Extensive numerical results are obtained and discussed in terms of characteristics lengths for the various transfer processes. Substantial effects of migration are seen in both the distribution of excited atoms near the cell windows and the line profile of the emergent radiation for typical laboratory conditions.     

The effect of oxygen on the sputtering of metastable atoms and ions from Ba metal

By means of the Doppler-Shift-Laser-Fluorescence technique we have measured the effect of oxygen coverage on the velocity distributions and relative yields of sputtered Ba atoms and ions in both the ground and metastable excited states. Our measurements show no evidence that the excitation probabilities are correlated with the magnitude of the electric-dipole-moment matrix element to the ground state. We also find that the excitation probability of the Ba(¹ D) state from a clean metal surface depends strongly on the emission velocity υ and approaches the functional form exp$\text{(}\text{?A}\text{av}\text{)}$ at higher velocities.     

激发态Na(3P)原子的碰撞缔合电离

用染料激光照射温度为250℃的Na蒸汽,将基态Na原子激发到3P态,两个Na(3P)原子碰撞,产生缔合电离,测量了缔合电离截面。本实验的关键是激发态原子密度及其空间分布的确定。本文用三种不同的方法测定Na(3P)原子密度,并仔细地研究了它们的空间分布;结合电离电流的测量,得到了缔合电离截面σ_Al=4.2×10^-17cm²(±36％)。与其它实验结果作了比较,并进行了讨论。 关键词：     

Continuous wave field ionization laser spectroscopy

A new technique is described which allows Doppler-free, isotope-selective excitation of atoms by continuous wave laser radiation and continuous ionization of the atoms by an electric field. The atoms are excited to high Rydberg states in an electric-field-free region of a collimated atomic beam. Because the lifetimes of Rydberg atoms are long they can reach a spatially separated region of the atomic beam where they are ionized by a continuous electric field with a probability of unity. In the case of lithium we obtained a 10³ times larger ion signal by field ionization of Rydberg atoms than by direct photoionization from low excited states.     

高电荷态离子126Xeq+与Ti固体表面作用的激发光谱

报道用150keV的高电荷态离子¹²⁶Xe^q+（6≤q≤30）轰击Ti固 体表面产生2 00—1000nm波段发射光谱的实验结果.结果显示，用电荷态足够高的离子作光谱激发源，无 需很强的束流强度（nA量级），便可激发起样品表面的原子和离子在可见光波段的特征谱线 .当入射离子剥离度q>q_c≈20时，Ti原子及其离子的特征谱线强度突然显著增强 ；不 同金属靶，特征谱线突然增强的q_c值不同.理论分析表明，这与q大于此临界值 后，单电子转移释放能量激发靶材料传导电子气体的表面等离激元密切相关. 关键词： 低速高电荷态离子 特征谱线 经典过垒模型 等离激元     

A comparison of radiation from sputtered atoms with radiation from projectiles scattered on oxidized magnesium at varying angle of incidence

The intensity of light emitted from sputtered atoms and neutralized, scattered primary ions, excited during 4 keV Ne⁺ and Ar⁺ bombardment of oxidized magnesium has been measured as a function of the incidence angle. It was found that the photon yield of sputtered atoms increases with the angle of incidence much more rapidly than the theoretical sputtering yield and the photon yield of scattered projectiles. In order to explain the experimental results a numerical approach was made based on the following assumptions: (1) the sputtered atom can be excited when it crosses the surface after getting the momentum from the collision cascade; (2) at oblique incidence the sputtered excited atom can be directly emitted after a gentle collision between the incident ion and the surface atom; (3) the neutralized primary ion can only be excited in a violent collision with the surface atom.