Dissociative Excitation of the Even Quartet and Sextet Levels of the Manganese Atom by Collisions of Electrons with Manganese Diiodide Molecules

Dissociative excitation of even quartet and sextet levels of the manganese atom by electron collisions with manganese diiodide molecules was studied experimentally. Twelve excitation cross-sections for transitions from quartet levels and 23 cross-sections for transitions from sextet levels were measured at an incident electron energy of 100 eV. The optical excitation function (OEF) was recorded in the range of electron energies 0?100 eV for transitions originating at the 3d⁵4s4de⁶D_J levels. The potential channels of dissociative excitation in the range of low electron energies (E < 22 eV) were discussed.     

Many-electron character of Rydberg series converging to the ionization thresholds of the 4<Emphasis Type="Italic">p</Emphasis><Superscript>4</Superscript>5<Emphasis Type="Italic">s</Emphasis> states of KrII

The photoionization cross sections of the 4p shell and the 4s main level and 4p ⁴(³ P) 5s ⁴ P _{5/2, 3/2} satellite subvalence levels of KrII have been calculated in the 4s-near-threshold range of excitation energies from 28.48 to 28.70 eV. The calculation takes into account the core relaxation by the methods of the theory of non-orthogonal orbitals, the interaction between resonant states through autoionization channels by solving the complex secular equation, and the interaction between the channels of the continuous spectrum in all orders of the perturbation theory by the K-matrix method. Good quantitative agreement between the energy-integrated theoretical and experimental photoionization cross sections for the satellite levels has been obtained for the first time. It is shown that only simultaneous consideration of the above-mentioned effects leads to such agreement. The resonant structure of the photoionization cross sections in this excitation energy range is related to the autoionization decay of the 4p ⁴5s(⁴ P _1/2)np and 4p ⁴5s(² P _3/2)np Rydberg series. The specificity of this process is that both series manifest themselves not independently but owing to their strong electrostatic interaction with the prominent 4p ⁴(¹ D)5s ² D _5/2 6p _3/2 resonance, which lies in this excitation energy range.     

Excitation of the Yb II transitions terminating on the low-lying odd levels

Excitation of the transitions from the even levels of a singly charged ytterbium ion that terminate on the low-lying odd levels 4f ¹³(² F°)6s ^{2 2} F°, 4f ¹⁴(¹ S)6p ² P°, and 4f ¹³(² F°_7/2)5d6p(³ D)³[3/2]° is experimentally studied by measuring 51 excitation cross sections at an electron energy of 50 eV, and 16 optical excitation functions are determined within the electron energy range 0–200 eV. The largest magnitudes of the measured cross sections exceed 3 × 10^?17 cm².     

On the possibility of laser generation without inversion on the fine-structure levels of a helium atom

It is shown that laser generation is possible in principle upon coherent excitation according to the V-scheme of the (1s2p)³ P _j levels with j = 1, 2 of a helium atom from the (1s2s)³ S ₁ level of the same atom when the latter level is, in turn, populated by electron or proton impact.     

Excitation of resonance lines of the cadmium ion by monoenergetic electrons

The excitation of resonance lines at 226.5 and 214.4 nm, corresponding to the transitions 226.5 (5p ² P ₁ ^2/0 →5s ² S _1/2) and 5p ² P ₃ ^2/0 → 5s ² S _1/2, respectively, in the Cd⁺ ion upon collisions with monoenergetic electrons with an energy in the range of 4–130 eV is studied with high precision by a spectroscopic method in crossing beams. It is found that the dependence of the effective excitation cross sections of the resonance doublet components on the energy of the electrons has a distinct resonance structure. It is shown that the dominant mechanism responsible for this structure is the capture of an incident electron by a Cd⁺ ion with the simultaneous excitation of an electron from the subvalence 4d ¹⁰ shell to the autoionizing states of the Cd atom with their subsequent decay (directly or via cascade transitions) to resonance levels of the ion. The results obtained are compared with data from other experiments and with the results of the R-matrix strong-coupling calculation of 15 states and of semiempirical calculation using the Van Regemorter formula.     

Electronic excitation of Ar atoms to metastable states and from metastable to higher states

The formation of the metastable states 3p ⁵4s of the Ar atom by an electron impact and the electronic excitation from these states to the higher levels 3p ⁵4p ArI are investigated in detail. The electronic excitation cross sections are determined based on a previously proposed approach to generalization of experimental and theoretical results. The method proposed consists in interpolation over the entire set of cross sections for each of the investigated levels of the Ar atom (measured by us previously or taken from the literature) using the four-parameter approximation of the dependences of the cross sections on the energy of incident electrons.     

Manifestation of the Coster-Kronig effect in the near-threshold electron-impact excitation of the Cd<Superscript>+</Superscript> ion

The near-threshold portions of the energy dependences of the effective excitation cross sections of the resonance transition 4d¹⁰5p²P_1/2° → 4d¹⁰5s²S_1/2 and the two-electron forbidden transition 4d⁹5s²²D_5/2 → 4d¹⁰5p²P_3/2° in the spectrum of the Cd⁺ ion were investigated by the spectroscopic method in crossed electron and ion beams. In the region of energy splitting of the ²P° and ²D levels, a significant resonance contribution of the autoionizing states of cadmium (decaying during the Coster-Kronig process) to the effective excitation cross sections of the noted transitions was revealed for the first time. It is found that the resonance contribution manifests itself much more strongly for the forbidden transition in comparison with the more intense resonance transition; i.e., the manifestation of the Coster-Kronig effect in the electron excitation of ions depends strongly on the cross section of the direct process. It is ascertained that, during the Coster-Kronig process, the main contribution to the resonance excitation of both the resonance and the two-electron forbidden spectral transitions is from the low-lying terms of the series of autoionizing states 4d¹⁰5p(²P_3/2°)ns, md and 4d⁹(²D_3/2)5s²ns, md, which are in the splitting region of the ²P_{1/2, 3/2}° and ²D_{5/2, 3/2} levels, rather than from the high-lying atomic autoionizing states of cadmium, which are located near the ionization limits (corresponding to the and ²P_3/2° and ²D_3/2 levels).     

Behavior of the excitation cross sections of the perturbed series of the xenon atom

Behavior of the excitation cross sections of the perturbed 6s[3/2]_n°?np[1/2]₀ spectral series of the xenon atom is experimentally studied. By using the methods of extended electron beam and optical spectroscopy, the cross sections are measured and the optical excitation functions are recorded for the transitions of this series with n=6–13. A deviation of the dependence Q=f(n) from a power-law function is revealed, as well as changes in the form of optical excitation functions and in the nature of the branching caused by perturbation of the 7p[1/2]₀ level by levels of the 5p ⁵(² P _1/2°)6p configuration.     

Energy levels of ions of silver and rhodium isoelectronic sequences with <Emphasis Type="Italic">Z</Emphasis> < 86

The method of extrapolation of the parameter of a model potential for states of one electron (4f, 5s, 5p, 5d, 5f) above the core 1s ²2s ²2p ⁶3s ²3p ⁶3d ¹⁰4s ²4p ⁶4d ¹⁰ and one vacancy (4d ⁹) in the same core is applied to calculate the energy levels in the silver and rhodium isoelectronic sequences with the maximum nuclear charge Z = 86. The energy levels of Ag-and Rh-like ions were used for the calculation of the energies of resonance transitions to the ground state ¹ S ₀ in Pd-like ions. Good agreement between the theoretical and calculated energies of the resonance transitions in Pd-like ions indicates the reliability of the results obtained.     

Study of postcollision interaction upon electron-impact excitation of the magnesium atom

The excitation functions of the spectral lines of the MgI principal series in the VUV region (for the principal quantum numbers n = 4–7) are studied in experiments on collisions of electrons with magnesium atoms in the range of electron energies from the excitation thresholds to ～25 eV. The scatter in the electron energy was ～0.7 eV. Above the ionization potential, some singularities attributed to autodetachment and autoionization states were found in excitation functions. Shifts to higher energies with increasing n, which take place for the most significant singularity (maximum) relative to the autoionization state 3p4s ¹ P ₁ ^o , are explained by the important role played by this state in the population of the initial levels through the mechanism of post-collision interaction. The theoretical analysis of the experimental results based on the classical model of the postcollision interaction estimates the width of the autoionization state as ～0.45 eV, which is close to the data of other researchers.     

Excitation of even levels of erbium atoms without a change in the number of 4<Emphasis Type="Italic">f</Emphasis> electrons

The excitation of even levels of erbium atoms by slow electrons that occurs without a change in the number of electrons in the 4f shell is experimentally studied. The levels investigated belong to the 4f ¹²6s7s, 4f ¹²5d6s, 4f ¹²6s6d configurations. The cross sections measured at an electron energy of 30 eV lie within the range (0.2–18) × 10^?18 cm².     

Dissociative Excitation of the Odd Sextet Levels of the Cobalt Atom by Collisions of Electrons with Cobalt Dichloride Molecules

Inelastic collisions of slow electrons with cobalt dichloride molecules, leading to the formation of excited cobalt atoms in odd sextet states, are experimentally studied. At an incident electron energy of 100 eV, thirty six dissociative excitation cross sections are measured for levels belonging to the z⁶D°, z⁶F°, and z⁶G° terms. In the electron energy range of 0–100 eV, ten optical excitation functions are recorded. The full cross sections for the dissociative excitation of the cobalt atom levels and the contribution of cascade transitions to their population are determined. The cross sections for electron–molecule and electron–atom collisions are compared.     

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.     

Configuration interaction and radiative constants in spectra of argon-like Sc IV-Fe IX ions

The probabilities of the 3p ⁵3d, 3p ⁵4s?3p ⁶, 3p ⁵4p, 3s3p ⁶3d electric dipole transitions and radiative lifetimes of the 3p ⁵3d, 3p ⁵4p, 3p ⁵4s, and 3s3p ⁶3d levels are calculated for the Sc IV–Fe IX isoelectronic sequence.     

Analyse von Hyperfeinstrukturen des Eu151, Am241 und einiger 3 d-Elemente mittels „Exchange Polarization“

It is shown how several discrepancies in the optical hfs of the Eu can be understood as consequences of the exchange polarization of the inner and outers-electrons by the spin of the half filled (4f ⁷)-subshell, an effect which should produce additional magnetic fields at the nucleus. Thus from the two different values of the electronic splitting constanta _6s in the two Eu-II ground states the polarization field from the 6s-shell (Δ H _6s ) is determined to be ca. +260 KG, and the formal splitting constantσ (??3 mK) of the (4f ⁷)-subshell yields ca. ?350 KG for the fieldΔ H _(1?5) from the five innern s-shells (n=1?5) in good agreement with the strength of the inner field obtained from recent Mössbauer effect studies.Δ H _(1?5) is deduced to be approximately equal in all sufficiently analysed ground and excited configurations of the neutral and ionised Eu atom ((4f ⁷) 6s, 6p, 5d, 6s ² and 6s 6p). Other elements with half filled subshells (Am, Mn) show similar features in their optical hfs. For Am⁺ ((5f ⁷) 7s) ca. ?2200 KG are found for the inner field (Δ H _(1?6)). For several 3d-elements it was found that the agreement between the calculated polarization fields and those following from experimental results is better than assumed so far.     

Single-electron charge transfer and excitations at collisions between Bi<Superscript>4+</Superscript> ions in the kiloelectronvolt energy range

Pioneering theoretical data for single-electron charge transfer and excitations due to collisions between Bi⁴⁺ ions in the ground (6s) and metastable (6p) states are gained in the collision energy interval 5–75 keV in the center-of-mass frame. The cross sections of the processes are calculated in terms of the close-coupling method in the basis of two-electron quasi-molecular states for the Coulomb trajectory of nuclei. It is found that single-electron capture into the singlet 6s ² states of Bi³⁺ ions makes a major contribution to the charge transfer total cross section for Bi⁴⁺(6s) + Bi⁴⁺(6s) collisions (reaction 1), whereas single-electron capture into the singlet 6s6p states is the basic contributor to the total cross section in Bi⁴⁺(6s) + Bi⁴⁺(6p) collisions (reaction 2). In the collision energy interval mentioned above, the collision cross sections vary between 1.2 × 10^?17 and 1.9 × 10^?17 cm² for reaction 1 and between 3.8 × 10^?17 and 5.3 × 10^?17 cm² for reaction 2. In reaction 1, the 6s → 6p excitation cross sections vary from 0.6 × 10^?16 to 0.8 × 10^?16 cm² for the singlet channel and from 2.2 × 10^?16 to 2.8 × 10^?16 cm² for the triplet channel. The calculation results are compared with the data obtained in experiments with crossed ion beams of kiloelectronvolt energy. The fraction of metastable ions in the beams is estimated by comparing the experimental data with the weighted average theoretical results for the cross sections of reactions 1 and 2. From the data for the charge transfer cross sections, one can estimate particle losses in relativistic beams due to a change in the charge state of the ions colliding with each other in the beam because of betatron oscillations.     

Precision measurements of optical excitation functions for the cadmium atom

An experimental setup and a technique for the investigation of excitation of atoms by ultramonoenergetic electrons are described. The optical excitation functions are given for 14 spectral lines of the cadmium atom originating from the n ¹ S ₀, 5¹ P ₁, n ³ S ₁, 5³ P ₁, and n ³ D _j levels. More than 150 specific features are found in the energy dependences of the effective excitation cross sections measured from the excitation threshold to 16 eV. The most pronounced of these features are in good agreement with the fine structure observed previously. The main mechanisms of the initial-level population, namely, the direct transition of an electron from the ground atomic state to the initial level of a spectral line, the population of the initial levels due to the decay of short-lived states of a negative ion, and the cascade population, are separated. In the excitation functions of the lines originating from the n ¹ S ₀ levels, in the energy range from 10.9 to 12.4 eV, we observed for the first time an effect of postcollision interactions of emitted and scattered electrons in the vicinity of the thresholds of four autoionization states of the cadmium atom.     

Ionization,charge exchange,and excitation during collisions of sodium ions with argon

The absolute values of cross sections of ionization, charge exchange, and excitation during Na⁺-Ar collisions are measured in the ion energy range 0.5–10.0 keV. Experiments are performed by a modified method of transverse electric field and by the optical spectrometry method. The mechanisms for realization of inelastic channels are explained qualitatively on the basis of a schematic correlation diagram of diabatic quasi-molecular energy levels of a system of colliding particles. The quasi-molecular nature of interaction is revealed for excitation processes. The excitation mechanisms of collision partners are established. A noticeable contribution to the excitation of the 4s state of the argon atom comes from the cascade transition from upper-lying 4p and 3d levels. An oscillatory structure is observed in the excitation functions of atomic lines of ArI (104.8 and 106.7 nm). The shape of the curve describing the dependence of the charge-exchange cross section on the collision energy is explained by the presence of two nonadiabaticity regions. In the low-energy region (up to E = 2 keV), charge exchange is due to electron capture to the ground state as a result of Σ–Σ transitions, while Σ–Π transitions associated with the rotation of internuclear axis play the leading role in charge exchange in the energy range E > 3 keV. The contribution of a number of inelastic channel is estimated for the ionization process. It is found that the main contribution to ionization is associated with the decay of self-ionization states in an isolated atom.     

X-ray photoelectron spectroscopy of FeP phosphide

The structure of the outer and inner electron spectra of iron (2p, 3p, 3s, and 3d) and phosphorus (3s and 3p) atoms in FeP monophosphide is studied in detail by the X-ray photoelectron spectroscopy (XPS) method. On the basis of the analysis of the binding energy of electrons, as well as the parameters characterizing the structure of experimental spectra, a conclusion is made that Fe³⁺ (d ⁵) cations in FeP are stabilized in a state with intermediate value of the total spin (IS, S = 3/2). The range of values of intra-atomic parameters (10Dq, J _H ) is established in which the consideration of the high degree of covalence of Fe–P bonds may lead to the stabilization of (FeP₆)^15– clusters in the IS state.     

Measurement of isotope shifts of gadolinium levels by laser-induced fluorescence spectroscopy

The results of isotope shift measurements for the gadolinium atom both in a hollow cathode lamp and in an atomic beam are described. Using laser-induced fluorescence spectroscopy, the measurements were performed for four transitions, which are related to the configurations 4f⁷5d6s²⁹D to 4f⁷5d6s6p⁹D and 4f⁷5d6ss6p⁹FD.