Fine-structure measurements for highly excited F states of cesium

The fine-structure splittings of highly excited F-states in Cs were measured using high-resolution laser spectroscopy. The 12 and 13²F states were found to be inverted with splittings ΔE (12²F)=?522(3) MHz and ΔE (13²F)=?416(3) MHz.     

Change in the states of optically excited Rb atoms near sapphire surface

The changes in the states of excited Rb atoms approaching a single-crystal sapphire surface have been investigated by methods of laser-excitation spectroscopy and luminescence of Rb vapor in a cell with sapphire windows, the gap between which was varied from 250 to 500 nm. Upon resonant excitation of Rb atoms by two semiconductor lasers with powers of 20 and 40 mW, luminescence from optically excited 5D _3/2 and 5D _5/2 states and optically unexcited 6P _1/2 and 6P _3/2 states is observed. It is established that the luminescence intensity from unexcited states is only a few times lower than that from excited states, with allowance for the fact that excited atoms are rapidly and almost completely quenched on the sapphire surface. The found anomalously strong luminescence from optically unexcited 6P _J states is explained by their nonradiative occupation near the sapphire surface from optically excited 5P _J states, in which atoms fail to reach the sapphire surface because of the repulsion from it. This repulsion is due to the polarization interaction between sapphire and the atoms in the 5P _J states near the surface. Nonradiative transition from the 5P _J state to the 6P _J ^?1 state is accompanied by excitation of two optical phonons in sapphire.     

Luminescence spectrum in far wings of the resonance line of cesium atoms approaching a sapphire surface

The shape of the luminescence spectrum of Cs atoms flying near a sapphire surface is described phenomenologically for the detuning from the D2 line ranging within 5–50 cm^?1. The numerical fitting of one theoretical parameter and a small variation of another parameter ensures a satisfactory agreement with the experimental spectrum. The experimentally determined abnormally high intensity of the antistatic wing is explained by the effect of phase relaxation of the atomic transition, caused by fluctuations of the electric field of oscillating ions of the sapphire crystal lattice.     

Kinetics of formation of the excited states of krypton atoms and ions upon electron-induced desorption from a solid surface

The kinetics of formation of the excited states of the atomic krypton ion is studied in pure krypton at a low pressure. The excited states are formed due to the dissociation of excited molecular ions desorbed from a solid surface by an electron beam. The lifetimes of these ions and their dissociation channels are determined.     

Adsorption of cesium atoms at structural defects on sapphire surfaces

Results are presented from an experimental study of the adsorption of cesium atoms on sapphire surfaces and their photostimulated desorption. The adsorbed atoms are found to form chains on the surface which are localized near one-dimensional structural defects of the surface. One-dimensional adsorption is analyzed theoretically with different assumptions regarding the mobility of adsorbed atoms along a chain. A comparison of the theories with experimental data favors localized adsorption described in terms of a one-dimensional lattice gas model. The energy of adsorption for an isolated atom on a linear surface structural defect is 0.58 eV, while the energy of attraction between neighboring atoms in the chain is 26 meV. Zh. éksp. Teor. Fiz. 112, 362–370 (July 1997)     

Autler-Townes doublet in the absorption spectra for the transition between excited states of cold cesium atoms

Autler-Townes splitting in absorption spectra of the excited states 6 2 P 3/2-8 2 S 1/2 of cold cesium atoms confined in a magneto-optical trap has been observed.Experimental data of the Autler-Townes splitting fit well to the dressed-atom theory,by which the fact of the cold atoms dressed by cooling/trapping laser beams is revealed.The results of the theoretical fitting with experiment not only told us the effective Rabi frequency cold atoms experienced,but also could be used for measuring the probability amplitudes of the dressed states.     

Radiative transitions in the system of autoionizing levels of cesium atoms excited by electron impact

We study the energy dependences of electron excitation cross sections of the autoionizing levels (5p ⁵6s ²)² P _3/2 and (5p ⁵5d(³ P)6s)² P _3/2, as well as the autoionization cross sections of cesium atoms in the impact energy range from the excitation threshold to 600 eV. It is established that an increase in the excitation cross section of the ² P _3/2 levels (to 60% of the maximum value) and the deep minimum in the autoionization cross section observed in the energy region of 17–27 eV are caused by the predominance of the radiative decay channel for autoionizing levels with excitation thresholds above 17 eV. The high efficiency of the process is mainly related to the resonance excitation of these levels in the near-threshold energy region.     

Calculations of the excited states of atoms

The possibility of calculating the approximate wave functions of the excited states of a many-electron atom by means of extremalization of the variation functional is discussed. The calculation of helium 1s2s ¹ S and X-ray K-state of neon was carried out in this way assuming the wave functions expressed in the analytical form. The results obtained are satisfactory compared with those obtained by other methods as well as compared with experiment.The author would like to thank Dr. E. Antoník for many discussions on the problems of this paper and the management of the Institute of Technical Physics for its all-round support. He also thanks his wife and Mrs. K. Trnková for carefully carrying out the tedious calculations.     

Photodesorption of rubidium atoms from a sapphire surface

The optical properties of the GdRhGe compound have been investigated in a wide spectral range by ellipsometry. Self-consistent calculations of the electronic structure have been performed within the local electron spin density approximation with a correction to strong electron interactions in the 4f shell of gadolinium ions (LSDA+U method). The experimental dispersion relation of the optical conductivity in the region of interband light absorption is interpreted based on the results of calculating the electron densities of states.     

Photoionization spectra of silver atoms adsorbed on the surface of a ZnS single crystal

We have used photostimulated flash luminescence to study deep electronic states arising when silver ions Ag⁺ are deposited under high vacuum onto the surface of a ZnS single crystal, followed by creation of the conditions for neutralization of the silver ions. The flux density of the silver ion beam was 10⁷ cm⁻²·sec⁻¹. We have observed the appearance of two types of deep electronic states with photoionization energies 1.60 eV and 1.80 eV, arising after depositing the silver ions onto the surface of the ZnS single crystal. We have hypothesized that there may be two different preferred sites for adsorption of silver atoms on the zinc sulfide surface. The corresponding photoionization spectra of the adsorbed silver atoms have maxima at 775 nm and 690 nm. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 335–338, May–June, 2006.     

Electron-stimulated desorption of cesium atoms from cesium layers deposited on a germanium-coated tungsten surface

The yield and energy distribution of Cs atoms from cesium layers adsorbed on germanium-coated tungsten were measured, using the time-of-flight technique with a surface-ionization-based detector, as a function of the energy of bombarding electrons, germanium film thickness, the amount of adsorbed cesium, and substrate temperature. The threshold for the appearance of Cs atoms is ～30 eV, which correlates well with the germanium 3d-level ionization energy. As the electron energy increases, the Cs atom yield passes through a broad maximum at ～120 eV. For germanium film thicknesses from 0.5 to 2 monolayers, resonance Cs yield peaks were observed at electron energies of 50 and 80 eV, which can be related to the tungsten 5p and 5s core-level ionization energies. As the cesium coverage increases, the Cs atom yield passes through a flat maximum at monolayer coverage. The energy distribution of Cs atoms follows a bell-shaped curve. With increasing cesium coverage, this curve shifts to higher energies for thin germanium films and to lower energies for thick films. The Cs energy distribution measured at a substrate temperature T = 160 K exhibits two bell-shaped peaks, namely, a narrow peak with a maximum at ～0.35 eV, associated with tungsten core-level excitation, and a broad peak with a maximum at ～0.5 eV, deriving from the excitation of the germanium 3d core level. The results obtained can be described within a model of Auger-stimulated desorption.     

A note on ejection of surface atoms in single crystal sputtering

Angular distributions of atoms sputtered around nearest-neighbour directions are calculated within the Lehmann-Sigmund model, for isotropic and anisotropic velocity distributions of subsurface atoms. The contribution of subsurface atoms to the spot turns out to be small.     

Collective electronically excited states of a uniform chain of atoms

Electronically excited states of finite uniform chains of atoms were considered taking into account the influence of the continuous energy spectrum. Traditional quantum-chemical methods for calculating two-electron transitions between neighboring chain atoms were combined with the asymptotic theory of interactions between excited atoms and neutral particles and the mathematical apparatus of the theory of multiple scattering for taking into account intercenter transitions in an ensemble of interacting centers. Recurrence equations for describing energy zones containing symmetrical and antisymmetric excited state levels of chains with an arbitrary length were obtained. Depending on system parameters, different modes of the distribution of the electron density of collective excited states were possible. At a certain ratio between level shifts and exchange integral values, excited states with a uniform electron density distribution over all chain nodes could form for certain solutions. This was a fortuitous circumstance caused by the influence of the continuous spectrum. Such states appeared at small principal quantum number n values, they were similar to one-electron excitations of the type of Frenkel excitons, when an electron was localized near its Coulomb center. These conditions were rapidly disturbed as n increased, and one-electron excitations of a linear molecule were formed in the system (that is, limiting excitations of the type of Wannier-Mott excitons did not form).     

Electron-stimulated desorption of potassium and cesium atoms from an oxidized molybdenum surface

The yield and energy distributions of potassium and cesium atoms emitted in electron-stimulated desorption (ESD) from a molybdenum surface, oxidized to different extent and maintained at 300 K, have been measured by the time-of-flight technique with a surface ionization detector. The ESD threshold for potassium and cesium atoms lies around 25 eV, irrespective of molybdenum oxidation state. In the case of molybdenum coated by an oxygen monolayer, secondary thresholds at ∼40 and ∼70 eV have been observed, as well as atomic energy distribution tailing down to very low energies. The most probable kinetic energies of the atoms are a few tenths of one eV. The results are explained within a model involving Auger neutralization of the adsorbed alkali metal ions after the filling of the 2s O, 4s Mo, and 4p Mo core holes. The possibility of ESD of a neutral species as a result of oxide-cation core-level ionization has been demonstrated for the first time. Fiz. Tverd. Tela (St. Petersburg) 39, 758–761 (April 1997)     

On the lifetime of certain excited states of chemisorbed atoms

For the determination of the ESD (electron stimulated desorption) cross section, the deexcitation process of the adsorbate plays an important role. In this paper we calculate the decay rate of the neutral adsorbate which is excited to the antibonding state, taking into account the electron-hole excitations in the metal. A similar technique which was used by Nozieres and Dominicis for the X-ray emission problem is applied for the summation of the diagram expansion. The lifetime of the antibonding state is estimated by the use of a simple model for the electron-hole excitation spectrum.     

Spectroscopy of cesium atoms adsorbing and desorbing at a dielectric surface

We use evanescent waves in a counterpropagating beams configuration to study the adsorption/desorption processes at a Cs vapor/dielectric interface in a sealed cell. Atoms close to the surface are velocity-selectively spin-polarized before adsorption by an amplitude-modulated pump beam. We subsequently observe the contribution of the desorbed atoms to the probe-beam absorption by way of phase-sensitive detection. We measure the number of desorbing polarized Cs atoms as a function of the surface temperature. The analysis of results is done through a simple thermodynamical model for the atomic desorption and we discuss its validity to infer the adsorption energy of the cesium atoms on a fused-quartz surface. Received: 15 May 2002 / Revised version: 7 August 2002 / Published online: 15 November 2002 RID="*" ID="*"Corresponding author. Fax: +55-83/216-7513, E-mail: martine@otica.ufpb.br     

Population of excited atomic states and ionization in a nonequilibrium low-pressure cesium plasma

A system of nonlinear algebraic equations is found for the population of the 20 lowest cesium levels in a nonequilibrium low-pressure plasma, with an account of many elementary processes. The system of equations is solved on a computer. A comparison of the results with the experimental data in the literature shows satisfactory agreement. The solution yields, in addition to the level populations, the ionization coefficient and the density of molecular cesium ions. It is shown that the ionization yield under these conditions is maximal at the 6P_3/2 level, thereafter falling off rapidly, so that the 20 lowest levels are responsible for essentially the entire ionization yield, and neglect of the other levels does not cause an error in the calculated ionization coefficient.Translated from lzvestiya Vysshikh Uchebnykh Zave-denii Fizika, Vol. 12, No. 1, pp. 52–56, January, 1969.In conclusion, the author thanks A. M. Devyatov and T. N. Solov'ev for discussions of this study.     

Evaporative cooling of cesium atoms in the gravito-optical surface trap

We report on cooling of an atomic cesium gas closely above an evanescent-wave atom mirror. Our first evaporation experiments show a temperature reduction from 10 μK down to 300 nK along with a gain in phase-space density of almost two orders of magnitude. In a series of measurements of heating and spin depolarization an incoherent background of resonant photons in the evanescent-wave diode laser light was found to be the limiting factor at this stage.     

Dissipation of the energy of excited atoms located near an absorptive medium surface

The nonradiative process of transfer of the excited atom energy to an absorptive medium is considered. The probability of the nonradiative EL-transition is calculated for an excited atom placed near a macroscopic medium surface with the complex dielectric function ? (ω₀). In the limit of very small distances the discussed process yields a main contribution to the level weight and determines the lifetime of the excited state.