The vuv photoelectron spectra of atomic In and Tl

The photoelectron spectra of atomic indium and thallium have been obtained using a pseudo-atomic beam technique. Ionizations from the np, ns and (n ? 1)d shells (n = 5 for In and n = 6 for Tl) were observed using He(I) and HE(II) radiation. The (np)^?1 ionization results in a single ¹S₀ ionized state, whereas the (ns)^?1 and ((n ? 1)d)^?1 ionizations both result in states additional to those allowed for a one-electron ionization process. This is attributed to configuration interaction in the final ionized state.     

High-precision calculationsj of the 3,1 P 1 0 →1 S 0 E1 amplitudes for magnesium, calcium, and strontium

High-precision calculations of the ^3,1 P ₁ ⁰ (ns np→¹ S ₀(ns ²) E1 amplitudes were carried out for magnesium, calcium, and strontium (n=3, 4, and 5, respectively). The following results were obtained for the reduced matrix element 〈¹ P ₁ ⁰ ‖d‖ ¹ S ₀〉 of electric dipole moment operator: 4.03(2) au for Mg, 4.91(7) au for Ca, and 5.28(9) au for Sr. These matrix elements are necessary for calculating the van der Waals coefficients C ₆, which are used in evaluating the atomic scattering lengths. The latter determine the dynamics and stability of the Bose-Einstein condensate.     

Neutron proton interaction potentials from experimental phase shifts

As an application of the inverse scattering technique of Marchenko, the single channelnp potentials¹ P ₁,³ P ₁,³ D ₂,³ P ₀ and¹ D ₂ are generated. Phase shift analyses below 1 GeV of Virginia serve as input. In these analyses, the³P₀ and the¹D₂ channels contain inelasticities above pion threshold. This work makes the first application of Marchenko's technique to higher partial waves and to nonunitary scattering functions.     

Two-photon spectroscopy of ytterbium

Two-photon laser spectra of the Yb vapor have been obtained. Transitions to highly excited 4f¹⁴ 6sns¹S₀ and 4f¹⁴ 6snd ¹D₂ states are seen in direct two-photon excitation. Hybrid resonances involving 4f¹⁴ 6s6p ¹P⁰₁ and 4f¹⁴ 5d6s ³D₂ intermediate states lead to transitions to 4f¹⁴ 6sns¹S₀, 4f¹⁴ 6snp ³P⁰_2,1 and 4f¹⁴ 6snd ¹D₂ levels.     

The role of the configuration interaction in excitation of the Cd(II) principal series at electron-atom collisions

The excitation functions of Cd(II) spectral lines, namely, the lines of the 4d ¹⁰5s ² S _1/2?4d ¹⁰ np ² P ₃ ^2/0 (n≤10) principal series and the line corresponding to a transition from the Beitler level 4d ⁹(5s5p ¹ P ⁰)² P ₃ ^2/0 , are analyzed under the conditions of electron-cadmium atom collisions in the electron energy range from excitation thresholds to 400 eV. It is found that the excitation functions of the spectral lines attributed to transitions from the Beitler level are similar to those of the principal series lines corresponding to transitions from the 4d ¹⁰ np ² P ₃ ^2/0 (n=9, 10) levels nearest to the Beitler level. This similarity is explained by the significant admixing of the Beitler level to the initial levels of the principal series lines. It is shown that the admixing substantially affects the excitation functions of this series for the states more distant from the Beitler level (up to n=6).     

Phase control in a coherent superposition of degenerate quantum states through frequency control

We demonstrate a controlled phase change of π in a degenerate superposition by altering a laser frequency by only 10 MHz. The method relies on the preparation of an adiabatic state involving the M = ±2 and M = 0 states of the ³P₂ (J = 2) level of metastable neon. Dependent on the frequency, the preparation proceeds either by stimulated Raman adiabatic passage (STIRAP) or by coherent population trapping (CPT). In the former case the superposition is prepared by adiabatic transfer induced in an extended tripod linkage scheme. In the latter case population is optically pumped into the Zeeman manifold of the level ³P₂. The population which does not reach a dark state decays to the ground state of neon. The amplitudes and relative phases of the dark states differ for the two cases. The phase change is monitored using the method of phase-to-population mapping.     

Detection and study of Rb I Rydberg states

We describe the details of an experiment using an atomic beam of rubidium which allowed us to detect by field ionization techniques the np Rydberg states from n = 28 up to n = 78, to detect also ns and nd states using a Stark mixing, and for all of these detected states to check the classical law E_c = [16n^*4]^?1 concerning the critical ionizing electric field E_c. It turns out that for n as high as 65 this law is quite well verified.     

Relativistic theory of the electric quadrupole moment of a hydrogen-like atom in the <Emphasis Type="Italic">s</Emphasis>1/2 and <Emphasis Type="Italic">p</Emphasis>1/2 states

Relativistic analytical expressions are derived for the electric quadrupole moment induced by the hyperfine interaction of the electron with the nucleus of a hydrogen-like atom in the ns_1/2 and np_1/2 states. The magnetic dipole and electric quadrupole hyperfine interactions are taken into account. The calculations are performed using the generalized virial relationships for the Dirac equation in a central field. The dependences of the electric quadrupole moment on the nuclear charge Z and the principal quantum number n are analyzed. The induced quadrupole moments are compared with the nuclear quadrupole moments.     

Electron Scattering from Neon Via Effective Range Theory

Elastic cross-sections for electron scattering on neon from 0 energy up to 16 eV are analyzed by an analytical approach to the modified effective range theory (MERT). It is shown that energy and angular variations of elastic differential, integral and momentum transfer cross-sections can be accurately parameterized by six MERT coefficients up to the energy threshold for the first Feshbach resonance. MERT parameters are determined empirically by numerical comparison with large collection of available experimental data of elastic total (integral) cross-sections. The present analysis is validated against numerous electron beams and swarm experiments. The comparison of derived MERT parameters with those found for other noble gases, helium, argon and krypton, is done. The derived scattering length (for the s-partial wave) in neon, 0.227 a ₀, agrees well with recent theories; it is small but, differently from Ar and Kr, still positive. Analogue parameters for the p-wave and the d-wave are negative and positive respectively for all the four gases compared.     

A study of Rydberg np states of Cd I and the determination of cadmium evaporation heat

The np ³ P _{0, 1, 2} states of Cd I in the range n=15–60 were studied by three-stage laser excitation and electric-field ionization for the measurement of kinetics of cadmium evaporation. The saturated vapor pressure and the evaporation heat of cadmium in a temperature range of 300–535 K were determined.     

Population of 2p 55s levels of neon in He-Ne plasma: I. The evolution of mechanisms in the discharge and the afterglow

The spectroscopic study of population processes of neon 2p ⁵5s states was carried out in helium afterglow with small admixture of neon at PHe = 38.1 torr, [He]/[Ne]=10^?5 with pulsed discharge afterglow in helium with small admixture of neon (pressure equal to 38.1 mm Hg; ). It is established that the main mechanism of population of 3s ₂ level (in Paschen’s notation) in the discharge and the initial after-glow is the excitation transfer from metastable atoms of He(2¹ S ₀). The other three levels—3s ₃, 3s ₄, and 3s ₅—corresponding to 2p ⁵5s configuration are populated in the afterglow as a result of the dissociative recombination HeNe⁺ of ions with electrons. The same process is also the main channel of population of 3s ₂ level in the late afterglow phase, when the concentration of He(2¹ S ₀) atoms is small. The hypothesis of recombination mechanism is confirmed by observation of the response of line intensities to pulsed electron heating. The partial coefficients of dissociative recombination into 2p ⁵5s states are estimated.     

The study of photoionization of neon-like Ar IX

The photoionization of the ground state of neon-like is investigated and the autoionizing spectrum of 2s²2p⁵²P_1/2ns,nd and 2s2p⁶²S_1/2np Rydberg series of Ar IX are studied by using the Breit-Pauli Hamiltonian within the R-matrix theory combine with the QB method of Quigly-Berrington [L. Quigley, K.A. Berrington, J. Pelan, Comput. Phys. Commun. 144 (1998) 225]. We predict the energies and widths of four Rydberg series of Ar IX.     

Relativistic Hartree-Fock oscillator strengths for the lowest s→p and p→d transitions in the first few members of the Ag(I) and Au(I) isoelectronic sequences,with allowance for cope polarization

Relativistic, single-configuration Hartree-Fock oscillator strengths for the lowest ns²S_{$\text{1}\text{2}$}→np²P_{$\text{1}\text{2}$$\text{3}\text{2}$} and np²P_{$\text{1}\text{2}$$\text{3}\text{2}$}→nd²D_{$\text{3}\text{2}$$\text{5}\text{2}$} transitions in the first few members of the silver (n = 5) and gold (n = 6) isoelectronic sequences have been studied, both with and without allowance for core polarization. Core polarization is included by introducing a polarization potential in the one-electron Hamiltonian and by employing the corresponding correction for the dipole-moment operator in the transition matrix element. The results obtained are compared with available experimental data and the influence of core-polarization effects on oscillator strengths is discussed.     

Resonances at collisions of slow electrons with cadmium atoms and ions

Using the crossed-beam method and a hypocycloidal electron spectrometer, the energy dependence of the ionization cross section for the cadmium atom has been studied in the near-threshold region and the elastic scattering of slow electrons at an angle close to 180° by Cd⁺ ions was studied for the first time. Within the region under study (0–7 eV above the first atomic ionization potential), a resonance structure determined by the contribution of atomic autoionization states is revealed in both the ionization curve and differential cross section of elastic scattering. The structure in the measured curves has been analyzed with the use of data on the ejected-electron spectra obtained under the excitation of autoionization states of Cd atoms, as well as the data on the optical excitation functions for the atomic spectral lines at λ=430.7 nm (5¹ P ₁-8¹ S ₀), 515.5 nm (5¹ P ₁-7¹ S ₀), 298.0 nm (5³ P ₂-6³ D _j ), and 361.0 nm (5³ P ₂-5³ D _j ).     

Coherent trapping of populations upon excitation by the Λ-scheme in a weak magnetic field

We have studied the influence of a constant magnetic field on the possibility of the formation of dark states and on the behavior of the alignment of an ensemble of atoms with the filled ns shell the (n + 1)³ S ₁ state of which is excited by the Λ-scheme from states n ³ P ₁ and n ³ P ₂, which, in turn, are populated by means of an axially symmetric interaction.     

Interaction of trapped metastable excited He atoms with solid noble gases,Ne, Ar and Kr,investigated by EPR

Local metastable excited states are found in Ne, Ar and Kr cryocrystals as He gas-discharge products are trapped in the growing cryocrystals. These states are detected by EPR and are interpreted as being local metastable excitednp⁵(n+1)s³P₂ atomic-type states in Ne, Ar and Kr cryocrystals. Analysis of the results allows the following explanation of the observed effect to be given. For the Ne cryocrystal the effect is interpreted as a new phenomenon: quasi-resonance transfer of excitation energy from the metastable He 2³S₁ atom trapped in a growing neon cryocrystal to the exciton energy band of the neon crystal followed by the exciton self-trapping into the 2p⁵3p state and subsequent decay, ending in the 2p⁵3s³P₂ state recorded by EPR in our experiment. In the case of Ar and Kr cryocrystals the effect is explained as being due to an internal ionization of the cryocrystals by the excitation energy of trapped metastable He atoms, which implies the formation in the cryocrytal of a Rg⁺ ion and a free electron in the conduction band, whereupon the fast (of 10^?12 s) self-trapping reaction of a hole follows: Rg⁺+Rg→Rg ₂ ⁺ . Thereafter the dissociative recombination reaction Rg ₂ ⁺ +e→Rg ₂ ^** →Rg+Rg*(³P₂) could take place.     

Relativistic Hartree-Fock oscillator strengths for the lowest s→p transitions in the first few members of the Rb(I) and Cs(I) isoelectronic sequences,with allowance for core polarization

Relativistic single-configuration Hartree-Fock oscillator strengths for the lowest ns²S_{$\text{1}\text{2}$}→ np²P_{$\text{1}\text{2}$,$\text{3}\text{2}$} transitions in the first few members of the rubidium (n = 5) and cesium (n = 6) isoelectronic sequences have been studied, both with and without allowance for core polarization. The effect of polarization of the core of the atom or ion by the valence electron is included by introducing a polarization potential in the one-electron Hamiltonian and by employing the corresponding correction for the dipole-moment operator in the transition matrix element. The results obtained compare well with available experimental data and indicate a significant influence of core-polarization effects on oscillator strengths. The behaviour of the oscillator strengths for the low Z part of the isoelectronic sequences is discussed.     

Polarization phenomena upon excitation by the Λ-scheme and at an anisotropic population of lower levels

We have investigated the possibility of the formation of dark states and of the change in the sign of the alignment of an ensemble of atoms with the filled ns-shell the state (n + 1)³ S ₁ of which is excited by the Λ-scheme from states n ³ P ₁ and n ³ P ₂, which, in turn, are populated by means of an axially symmetric interaction.     

Wirkungsquerschnitte depolarisierender Stöße von angeregten Natriumatomen mit Edelgasatomen durch optisches Pumpen mitD 2-Licht

Optical pumping of sodium vapor withD ₂-light causes a rise of optical transparency if complete collision-induced mixing takes place among the sublevels of the excited² P-states. It causes a drop of optical transparency if there would be no mixing in the excited states. It causes no change of optical transparency if excited-state mixing is as strong as the condition 2T=3τ predicts,T being the mean collision time, τ the mean life time of the excited states. The latter case can be realized by certain buffer gas pressures. These pressures have been measured for the gases helium, neon, and argon. From these pressures excited state-mixing cross sections have been deduced by means of the quoted condition. Finally the so far used “uniform” mixing model has been critically revised. A more realistic model is proposed which ascribes excited-state-mixing to scattering phase shifts between the molecularσ- andπ-states into which the atomic² P-state splits during the collision. Nevertheless, the condition 2T=3τ is not seriously altered even in this refined model.