Measurement of the fine structure of the n = 4 state of hydrogen

A time-resolved spectroscopy technique has been used to measure the fine structure of the n = 4 state of hydrogen. The excited hydrogen atoms were formed by the use of an electron beam to dissociate molecular hydrogen. The resonance transitions were observed by keeping the radio frequency field fixed and sweeping the magnetic field. Measurements on deuterium were used to study the effects of pressure and motional electric fields. The ²S_1/2 → ²P_1/2 Lamb shift transition , the ²P_3/2 → ²S_1/2 fine structure interval ΔE − L, and the ambient electric field in the measurement volume were determined by using measurements on three separate transitions made at fixed magnetic field. The measurements gave and     

Measurement of the fine structure separation in the 42 D term of lithium by the method of electric field induced level anti-crossing

An electric field is employed to convert lithium 4² D Zeeman level crossings into anti-crossings. The lithium atoms are excited by electron impact. The anti-crossings are detected by the change in polarization of the light emitted in the 4² D-2² P transition. From the corresponding values of the magnetic field, we obtain 400 (10) MHz for the zero field fine structure energy separationE(4² D _5/2)-E(4² D _3/2).     

Complex structure of resonant coherent excitation peaks for heavy relativistic hydrogen-like ions under planar channeling

The computer model for the resonant coherent excitation of heavy relativistic ions under planar channeling in crystals taking into account the fine structure of the energy levels of the orbital electron and the ion ionization from both the ground and first excited state is presented. The model has been used to explain the experiments carried out under planar channeling of 390 MeV/n ¹⁷⁺Ar ions. Reasonably good agreement for the calculated and experimental data has been obtained.     

Fine-structure in secondary electron emission from Cu(0 0 1)c(2 × 2)-Cl: Experiment and theory

Normal emission secondary electron spectra excited by photons of energy ?ω = 21.2 eV and by electrons of 100 eV kinetic energy have been measured with high resolution from Cu(0 0 1) and Cu(0 0 1)c(2 × 2)-Cl. Calculations were performed using a “one-step” multiple scattering formalism for the semi-infinite system. The close agreement between experimental and theoretical fine structure reveals the nature of individual features. Our results demonstrate that in general bulk-derived features in the secondary electron fine structure cannot be directly associated with critical points in the band structure.     

Reappearance of fine structure as a probe of lifetime broadening mechanisms in the 4f(N) --> 4f(N-1)5d excitation spectra of Tb3+, Er3+, and Tm3+ in CaF2 and LiYF4

High-energy transitions in the 4f(N) -->4f(N-1)5d excitation spectra of lanthanide ions in host crystals are usually broadened due to the short excited-state lifetimes, whereas low-energy transitions, with longer excited-state lifetimes, may show fine structure. We report the surprising observation that for some materials fine structure is observed not only for the low-energy excitation bands but also for some high-energy transitions. The excited states that display fine structure are those for which the 5d electron is in the lowest crystal-field level but the 4f(N-1) core is in a highly excited state, indicating that the broadening depends only on the energy of the 5d electron and not on the total energy of the 4f(N-1)5d excited state.     

Photoacoustic Spectra Studies on Neodymium Complexes

A series of neodymium complexes crystals were synthesized and their photoacoustic spectra were determined. The excited state energy levels of Nd(III) in different complexes were discussed and their relaxation processes were studied. The different coordination environments were shown by comparing the band due to Nd(III) ⁴19/2 – ⁴G5/2, C7/2 transitions in different complexes. The fine structure of this absorption shows that the Nd-0 bond forms a stronger coordinated bond than that of Nd-N system.     

Visible spectra of heavy ions with an open 4f shell

We present visible to near-infrared spectra of highly charged Yb (the atomic number 70) and W (74) obtained with a compact electron beam ion trap. By observing the dependence on the electron beam energy, the charge state that should be assigned to the observed lines is determined. For In-like Yb²¹⁺ and W²⁵⁺ and Sn-like W²⁴⁺, the experimental spectra are compared with theoretical calculations done by the CI+all-order method. In each spectrum, the most prominent line is identified as the magnetic dipole transition from the first excited fine structure level to the ground level in the ground electronic configuration, 4f³ for In-like ions and 4f⁴ for Sn-like ions.     

Nuclear reactions as an example of the quantum theory of irreversible processes

A modification of the atomic beam magnetic resonance method for investigation of the hyperfine structure of excited atomic states will be described. Radiofrequency transitions between the hyperfine structure niveaus of the excited state, which are unequally populated by circularly polarized light, are detected by observing the resulting change in population number of the hyperfine structure niveaus of the ground state using magnetic deflection in an inhomogeneous field and additional radiofrequency transitions in the ground state as analyzers. As an application the hyperfine structure of the excited 4² P _3/2-state of K³⁹ has been investigated in an almost strong magnetic field of about 65 G with a constant frequency of the applied radiofrequency field of 125.50 Mc/s. The analysis of the radiofrequency signal of the excited state detected as a change in the amplitude of a radiofrequency transition in the ground state yielded the valuesA=(6.10±0.25) Mc/s andB=(1.8±1.2) Mc/s for the hyperfine structure constants of the 4² P _3/2-state of K³⁹. Further possibilities for observing signals of the excited state with the apparatus used in this experiment are also discussed.     

Spatial distribution of dynamic mechanical stresses in ionic crystals under the action of a pulsed electron beam

We report on the results of experimental and theoretical investigation of the shape of an acoustic pulse generated in alkali-halide crystals by a pulsed electron beam with a maximal electron energy of 0.28 MeV and an energy density of 0.10–0.65 J/cm². It is found that the shape of the acoustic pulse for the given beam parameters substantially differs from the absorbed energy density profile. The formation of the fine structure of the acoustic pulse is associated with local release of energy due to the evolution of multichannel electrical breakdown.     

Rotational structure of the origin band in the 1A′ ←X1σ+ electronic transition of C4H− and C4D−

The rotational structure of the origin band for the ¹A′←X¹σt⁺ electronic transition, lying just below the electron affinity of C⁴H, was recorded by means of a two-colour resonant photodetachment technique. This allowed a determination of the rotational constants in the X¹σt⁺ ground and ¹A′ dipole bound excited state. The low lying A²II excited state of C⁴H is inferred to be the parent of the dipole bound state. The excited electronic state is deduced to have a nonlinear planar structure whereas the ground is linear according to the spectral analysis. The rotational constants have been obtained: B′; = 0.1552(2)cm^?1 for the X¹σt⁺ state, and A′ = 30.73(1), B′ = 0.1587(2), C′ = 0.1581(2)cm^?1 for the ¹A′ state.     

On the nature of emissions of polymethyl methacrylate excited by an electron beam of subnanosecond or nanosecond duration

The results of studies of the physical nature of emissions produced in polymethyl methacrylate excited by electron beams of a subnanosecond or a nanosecond duration are presented. The spatial, amplitude, and spectral-kinetic properties of emissions have been examined under an electron beam energy density varying from 10^–4 to 4 × 10^–1 J/cm². It has been found that cathodoluminescence is the primary type of emission under low energy densities of the electron beam. When the energy density of a nanosecond electron beam and/or the number of pulses of excitation by a subnanosecond electron beam were increased, an electrical breakdown of polymethyl methacrylate occurred in the irradiated region. This process was accompanied by a burst of emission of dense, low-temperature plasma.     

Magnetic field effect on the luminescence of the paired Ag- ions in alkali halides (II)

The fine structure of the relaxed excited state of paired Ag^- ions in KBr and RbBr is studied by measuring the magnetic field effects on the decay time of the luminescence at about 2 K. The experimental results obtained are found to be well explained theoretically by assuming thermal equilibrium, with the exception of an anomalous change at about 43 kG(KBr) or at about 34 kG(RbBr). The anomalous change exhibits a level crossing and also shows that the Zeeman levels do not reach the thermal equilibrium at least in the neighborhood of the level crossing.     

Excited high spin states of novel π conjugated verdazyl radicals: photoinduced spin alignment utilizing the excited molecular field

This paper reports the excited quartet (S = 3/2) and quintet (S = 2) states arising from the intramolecular radical-triplet pair in the purely organic π conjugated spin systems. A previous paper reported the excited quartet and quintet states of 9-anthracene-(4-phenyliminonitroxide) and 9,10-anthracene-bis(4-phenyliminonitroxide), respectively, in which iminonitroxide radicals are linked to the phenyl- or diphenylanthracene moiety (a spin-coupler) through the π conjugation. The similar excited quartet and quintet states were observed for the 9-anthra-cene-(4-phenylverdazyl) radical (1) and 9,10-anthracene-bis(4-phenylverdazyl) diradical (2) by time resolved electron spin resonance (TRESR). The TRESR spectrum was analysed by the ordinary spin Hamiltonian with the Zeeman and fine structure terms. For the quartet state of 1, the g value, fine structure splitting, and relative population of the Ms sublevels have been determined to be g = 2.0035, D = 0.0230 cm^?1, E = 0.0, P _1/2′ = P _?1/2′ = 0.5 and P _3/2′ = P _?3/2′ = 0.0, respectively, by spectral simulation. The spin Hamiltonian parameters of the quintet state of 2 were determined to be g = 2.0035, D = 0.0128 cm^?1, E = 0.0, P _2′ = P _?2′ = 0.0, P _1′ = P _?1′ = 0.37 and P _0′ = 0.26, respectively. Direct observation of the excited high spin state showed that photoinduced intramolecular spin alignment is realized between the excited triplet state (S = 1) of the phenyl- or diphenylanthracene moiety and the doublet spin (S = 1/2) of the dangling verdazyl radicals. Ab initio MO calculations (DFT) were carried out in order to clarify the mechanism of the photoinduced spin alignment.     

Polarization effects in theP 3/2→P 1/2 fine structure transition cross section forK(4P)-He collisions

Taking the energy dependence of theP _3/2→P _1/2 fine structure transition cross section ofK(4P) colliding with He as an example, theoretical and experimental studies have been made to illustrate the large possibilities opened by the combination of beam experiments with laser excitation in the investigation of the atomic collisional processes. Explicit calculations, experimentally confirmed, show a strong dependence of the above process on the laser excitation schema for producing the excited stateK(4² P _3/2).     

High energy excitations in ion-induced electron emission from AlF3

Measurements of electron emission spectra from surfaces of aluminum fluoride impacted by keV noble gas ions show a high-energy structure, peaking around 7 eV that increases in intensity with ion energy. The shape of this structure, identified by Factor Analysis, is independent of the nature and the energy of the impinging ions. We discuss one electron, two electron and plasmon excitation mechanisms and conclude that the high-energy structure results from the autoionization of F^? 2p⁴nl n′l′ excited by electron promotion in close atomic collisions.     

Peculiarities in fragment mass distribution in the 238U + 40Ar (243 MeV) reaction

A pronounced fine structure (FS) in the form of distinct peaks was observed in neutron gated mass spectra from the decay of the ²⁷⁸110 composite system produced in the reaction ²³⁸U + ⁴⁰Ar (243 MeV) at an initial excitation energy E ^* > 70 MeV. The FS peaks are located in the vicinity of mass numbers 70-80, 100, and 130, which correspond to those of magic nuclei (clusters). In the data there is also evidence for a new type of decay -- collinear cluster tripartition of an excited nucleus. Received: 8 August 2000 / Accepted: 2 February 2001     

Role of the Ce<Superscript>2+</Superscript> ions in cerium fluoride luminescence

Pulsed cathodoluminescence (PCL) of CeF₃ crystals was studied using a KLAVI-type setup. PCL was excited by bombarding samples in air at room temperature using a 2-ns pulsed electron beam at an electron energy of 170 keV, current density of 160 A/cm², and repetition rate of 2.5 Hz. Luminescence and phosphorescence were observed in the UV and visible spectral regions. The phosphorescence is tentatively associated with the Ce²⁺ ion formation.     

Detailed spectroscopy in the superdeformed second minimum of 240Pu

Spectroscopic studies in the superdeformed shape isomer of ²⁴⁰Pu using γ-spectroscopy, conversion electron spectroscopy and transmission resonance spectroscopy have been performed. In a high-resolution and high-efficiency γ-spectroscopy experiment the out-of-band decays of several excited superdeformed rotational sequences with K=2^? and 1^? could be identified together with evidence for a weakly populated 0^? octupole band. Surprisingly, no low-lying collective quadrupole excitations could be observed. Complementary information could be obtained in conversion electron measurements in coincidence with isomeric fission, resulting in the first identification of the lowest ß-vibrational K=0⁺ band. For all rotational bands the variation of the moment of inertia with spin could be studied. A predominant population of negative parity states in the second well could be observed, which can be explained by the selective population and depopulation of the second minimum. Complementary transmission resonance measurements have been performed, yielding new information on the fine structure of high-lying (ß-)vibrational multi-phonon states. A new method could be established to determine the excitation energy of the fission isomer ground state from measured level densities.     

New possible laser media in the UV and XUY in high current heavy ion beam induced plasmas

Mixtures of rare gases with alkali-metal vapour were excited by a high power argon ion beam in a windowless gas target system. Narrow emission continua were observed in the vacuum ultraviolet region between 60 and 200 nm. The observed emission was assigned to the decay of a new class of excited ionic molecules Rg⁺ A formed by the combination of a rare gas ion Rg⁺ with an alkali atom A. These excimer-like ions are of great interest for possible short-wavelength lasers, because the ground state consisting of a rare gas atom and an alkali ion is only weakly bound. The observed decay energies and fine structure splittings agree well with the prediction of calculations. A summary of previous results is presented.Supported by the German Government Department for Research and Technology (BMFT), Bonn, Germany.     

Advances in laser spectroscopy of lithium

A number of recent experiments have employed novel spectroscopic techniques to precisely measure the fine and hyperfine structure splittings as well as the isotope shifts for several transitions at optical frequencies for the stable ^6,7Li and radioactive isotopes ^8,9,11Li. These data offer an important test of theoretical techniques that have been developed over the last decade by two groups to accurately calculate effects due to Quantum Electrodynamics and the finite nuclear size in 2 and 3 electron atoms. Theory and experiment have studied several transitions in both singly ionized and neutral lithium. The work by multiple groups permits a critical examination of the consistency of separately, the experimental work as well as the theoretical calculations. Combining the measured isotope shifts with the calculated energy shifts passing these consistency tests, permits the determination of the relative nuclear charge radius with an uncertainty approaching 1 × 10^?18 meter. These results are more than an order of magnitude more accurate than those obtained by electron scattering experiments and give insight into the mass and charge distributions of the nuclear constituents. Prospects for a precision measurement of the fine structure constant are also discussed.