Excited Ionic States Research Articles

Electron-Iron Recombination Rate Coefficients and Photoionization Cross Section for S XIV and SXV for X-ray and UV modeling

The inverse processes of photoionization and electron-ion recombination of (hv + S XIV 1:::; S XV + e) and (hv + S XV =r SXVI+ e) are studied in detail using ab initio unified method that provides self-consistent sets ofresults for these processes. Results are presented for large number of fine structure levels where n S 10 and 0 ~ l ~ 9; 98 levels for Li-Iike S XIV with 1/2 S J ~. 17/2 and 188 levels for He-like S XV with 0 ::;J ~ 10. Photoionization cross section, O'PI, of the levels of both S XIV and S XV decay smoothly in the lower region. However, narrow and high peak autoionizing Rydberg series of resonances belonging to various excited core levels appear in the high energy region and enhance the background cross section of the excited levels. The resonance series of n=2 core levels dominate while they become weaker with higher n. The prominent feature is the enhancement of the background cross section at n=2 core thresholds due toK-shell ionization leaving the ion in excited 2p states. 0' PI also show wide PEe (photo-excitation-of-core) resonances at the photon energies that equal to the core excitation energies. Level-specific photoionization cross sections, O'PJ(nSLJ), and recombination rate coefficients, QRc(nSLJ), are obtained for the first time for theseions. Currently available results correspond to photoionization for L8 terms with missing features and to only total recombination rate coefficients. Present QRc(nSLJ) incorporates both the radiative recombination. (RR) and dielectronic recombination (DR), and show a 'bump' or 'shoulder' in the high temperature region due to DR dominance. The total unified recombination rate coefficients show good agreement with the availableRR and DR rates. Recombination rates over photoelectron energy are presented for astrophysical and laboratory plasma applications. Total recombination rates for H-like S XVI are given for completeness. The results should be accurate within 10-15% based on the unified method that includes important atomic effects such as radiation damping, channel couplings, interference of DR and RR, and relativistic fine structure effects. The comprehensive datasets are applicable for various models such as for ionization balance and recombination-cascade for UV'and X-ray lines.

Electronic State Spectroscopy of c-C5F8 Explored by Photoabsorption, Electron Impact, Photoelectron Spectroscopies and Ab Initio Calculations

The electronic transitions and resonance-enhanced vibrational excitations of octafluorocyclopentene (c-C5F8) have been investigated using high-resolution photoabsorption spectroscopy in the energy range 6-11 eV. In addition, the high-resolution electron energy loss spectrum (HREELS) was recorded under the electric dipolar excitation conditions (100 eV incident energy, approximately 0 degrees scattering angle) over the 5-14 eV energy loss range. A He(I) photoelectron spectrum (PES) has also been recorded between 11 and 20 eV, allowing us to derive a more precise value of (11.288 +/- 0.002) eV for the ground neutral state adiabatic ionization energy. All spectra presented in this paper represent the first and highest resolution data yet reported for octafluorocyclopentene. Ab initio calculations have been performed for helping in the assignment of the spectral bands for both neutral excited states and ionic states.

Formation of excited states of atoms and ions in laser plasma from CuInS2

Emission spectra and the energy distribution of the excited-state population density of atoms and ions in erosion laser plasma from CuInS2 with various crystal-structure orderings are analyzed. It is shown that increased ordering of the target crystal structure causes the excited-state energies of indium atoms generated in the laser erosion plume to increase and that sulfur atoms always emit only in transitions from highly excited states. The ratio of relative ion concentrations in the laser plasma plume is Cu+/In+/S+ = 0.3/0.08/2, which corresponds neither to the atomic ratio of Cu/In/S (1/1/2) in the target nor to the ratio of ionization energies. The results are explained by recombination processes for ions and by the atomization specifics of the CuInS2 target exposed to long-wavelength radiation. The atomization consists essentially of dissociative processes expressed by CuInS2 → CuInS + S and CuInS2 → Cu + InS + S. The electron temperature of polycrystal (single-crystal) plasma at a distance of 1 mm from the target is 0.3 eV (0.4 eV) for atoms and 1.3 eV (2.7 eV) for ions and varies negligibly for plasma up to a distance of 7 mm from the target.

Photodissociation/photoionization processes of chlorobromomethane induced by femtosecond laser pulses with pump-probe scheme

The photodissociation/photoionization processes of chlorobromomethane (CH2BrCl) induced by femtosecond laser pulses have been investigated using pump-probe scheme combined with the time-of-flight mass spectra. The dominate photoproducts are observed at different delay time of the pump (400 nm) and probe (800 nm) pulses and the corresponding time-dependence of them is obtained. The results show that the decaying time of the molecule CH2BrCl in the A-band is in the 100 fs. The decaying tendencies of the fragment ions (CH2Cl+ and CH2Br+) and the parent ion (CH2BrCl+) are almost the same and the relative ratios of the yields of them keep constant during the delay time of 0 to 150 fs. These facts suggest that the fragment ions come from the fragmentation of the parent ions in excited electronic states. The probabilities to form CH2Cl+ and CH2Br+ are obtained from the relative ratio of the ion intensity and are about 71.6% and 14.2%, respectively.

Dynamics of electron emission in double photoionization processes near the krypton 3d threshold

Two-electron emission following photoabsorption near the Kr 3d threshold is investigated both experimentally and theoretically. On the experimental side, electron/electron coincidences using a magnetic bottle time-of-flight spectrometer allow us to observe the complete double photo ionization (DPI) continua of selected Kr2+ final states, and to see how these continua are affected by resonant processes in the vicinity of the Kr 3d threshold. The analysis is based on a quantum mechanical approach that takes into account the contribution of three different processes: (A) Auger decay of the inner 3d vacancy with the associated post-collision interaction (PCI) effects, (B) capture of slow photoelectrons into discrete states followed by valence multiplet decay (VMD) of the excited ionic states and (C) valence shell DPI. The dominant process for each Kr2+(4p−2) final state is the photoionization of the inner shell followed by Auger decay of the 3d vacancies. Moreover, for the 4p−2(3P) and 4p−2(1D) final ionic states an important contribution comes from the processes of slow photoelectron capture followed by VMD as well as from double ionization of the outer shell involving also VMD.

Effect of ionization and recombination between excited states on gain of 19.6nm X-ray laser

As it is difficult to solve a large number of rate equations including doubly excited states of various ions, block matrix method is expected to dramatically reduce the machine time by dividing the large number of equations into pieces of small units, and solving them one by one, on condition that the ionization and recombination between excited states of ions can be ignored. In this paper, the influence of ionization and recombination between excited states on plasma status was studied, and detailed analysis of its mechanism was made. The effect on gain of Ne-like Ge 19.6nm X-ray laser respectively driven by 1.0ns pulse, 100ps pulse and 5ps pre-pulse and main pulse was studied. The simulation shows that for the 5ps driving pulse case, the ionization and recombination between excited states has relatively large influence, and it can not be ignored and that for the two quasi-stable state cases, in the gain region with electron density less than 5×1020cm－3, the FWHM temporal width of gain increases by～10%, and the FWHM spatial width of gain increases respectively by～13% and ～-23%, and the time the peak gain appears is delayed respectively by～1.4% and ～6.9%, which is tolerable, implying that the block matrix method could be applied in the qualitative modeling of QSS scheme X-ray laser. However, for accurate study, the ionization between the excited states could not be neglected.

The VUV electronic spectroscopy of acetone studied by synchrotron radiation

The electronic state spectroscopy of acetone (CH3)2CO has been investigated using high-resolution VUV photoabsorption spectroscopy in the energy range 3.7-10.8 eV. New vibronic structure has been observed, notably in the low energy absorption band assigned to the 1(1)A(1) --> 1(1)A2 (ny --> pi*) transition. The local absorption maximum at 7.85 eV has been tentatively attributed to the 4(1)A1 (pi --> pi*) transition. Six Rydberg series converging to the lowest ionisation energy (9.708 eV) have been assigned as well as a newly-resolved ns Rydberg series converging to the first ionic excited state (12.590 eV). Rydberg orbitals of each series have been classified according to the magnitude of the quantum defect (delta) and are extended to higher quantum numbers than in the previous analyses.

On the atomic particle concentration ratio in a multicomponent laser plasma plume

The occupancy distribution for the excited states of atoms and ions is derived based on emission spectroscopy data for an erosion plasma arising when laser radiation strikes a solid CuSbS2 target. The ratios between the copper and sulfur concentrations in the laser plume at distances of 1 and 7 mm from the target are compared. It is shown that the copper atom-to-sulfur ion concentration ratio in the laser plasma decreases with distance from the target.

Effects of argon-ion bombardment on the properties of the surface layer in spinel crystals of different composition

Ion-induced photon emission (IPE) during bombardment of magnesium aluminate spinel crystals MgO· nAl 2O 3 by 20 keV Ar + ions was studied. The dependence of the yield of particles in specific excited states on the fluence of incident ions in the range of (0.1–1.6)×10 17 ions/cm 2 was measured. It was shown that yield of magnesium and aluminum atoms and ions in most excited states do not depend (or slightly depend) on the fluence of ion bombardment. An exception was found for yields of Mg + ions in the 4s 2S excited state and Al atoms in the 5p 2P 0 excited state leading to emission lines at 292.8 and 669.6 nm, respectively. The yield of particles in these excited states drastically decreases at the start of ion bombardment. Analysis of these results and published data on the bombardment-induced surface modification of spinel crystals allows to elucidate the role of crystal structure and chemical bonding in the formation of some excited states. The dependence of excited state yield (except of Mg and Al indicated above) from spinel crystals of different composition MgO· nAl 2O 3 ( n=1.0, 1.5, 2.0, and 2.5) does not reflect quantitatively the variation of the calculated bulk concentration of constituent atoms in these targets.

Charge exchange of multiply charged laser plasma ions with rare-gas jet atoms

The interaction of a gas jet (He, Ne, Xe) with the incident laser plasma from a solid target [B, (CH2)n, (CF4)n] removed by ≈1 cm is investigated. Line spectra arising from the charge exchange of multiply charged plasma ions with rare-gas atoms are recorded in the multiply charged ions–gas interaction region. The ratios between the partial cross sections of the charge exchange with the production of these ions in excited states are determined from the relative intensities of the Balmer series transitions in BV and CVI ions. These results are compared with theoretical data.

A study of vibronic coupling in neutral and ionic states of carbon disulphide

Dispersed fluorescence spectroscopy has been employed to study vibronic coupling in neutral and ionic states of carbon disulphide. The vibrationally resolved excitation spectra of the , , and transitions have revealed new structure and possible assignments are discussed. Autoionization from vibrationally unexcited Rydberg states belonging to series converging onto the limit appears to result in the formation of vibrationally excited state ions, including those with one or two quanta of the antisymmetric stretching mode. Most of the bands in the dispersed fluorescence spectrum have been assigned using energy levels determined in photoelectron spectroscopic studies. The four subbands associated with the Renner–Teller split vibronic transition have been identified.

High-temperature behaviour of the helium-like K G ratio: the effect of improved recombination rate coefficients for calcium, iron and nickel

It is shown that above the temperature of maximum abundance, recombination rates into the excited states of He-like ions that are calculated using earlier, more approximate methods differ markedly from rates obtained from recent distorted-wave and R-matrix calculations (unified recombination rate coefficients) for Ca, Fe and Ni. The present rates lead to G ratios that are greatly lower than those resulting from the more approximate rates in previous works, by up to a factor of 6 at high electron temperatures. Excellent agreement between the distorted-wave and the R-matrix rates, as well as excellent agreement in the G ratios calculated from them, provides support for the accuracy of these new values which have a broad applicability to the modelling and interpreting of X-ray spectra from a variety of astrophysical and laboratory sources.

Perfluorocyclobutane electronic state spectroscopy by high-resolution vacuum ultraviolet photoabsorption, electron impact,HeIphotoelectron spectroscopy, andab initiocalculations

The electronic state spectroscopy of perfluorocyclobutane $(c\text{\ensuremath{-}}{\mathrm{C}}_{4}{\mathrm{F}}_{8})$ has been investigated using high resolution vacuum ultraviolet (vuv) photoabsorption spectroscopy in the energy range $6.0--11\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The electron energy loss spectrum (EELS) was also recorded in the nonelectric dipolar interaction mode ($100\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ incident energy, 10\ifmmode^\circ\else\textdegree\fi{} scattering angle) over the $8--14\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ energy-loss range and the excited states in the $11--14\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ spectral region have been observed. An $\mathrm{He}\phantom{\rule{0.2em}{0ex}}I$ photoelectron spectrum recorded between 11.0 and $19.8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ is compared with earlier lower resolution results. This has allowed us to derive a more precise value of $12.291\ifmmode\pm\else\textpm\fi{}0.002\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for the ground neutral state vertical ionization energy. All spectra presented in this paper represent the highest resolution data yet reported for perfluorocyclobutane, to the best of our knowledge. Ab initio calculations have been performed for helping in the assignment of the spectral bands for both neutral excited states and ionic states.

Electron capture into few-electron heavy ions: Independent particle model

We apply the density matrix theory to re-investigate the radiative electron capture into heavy ions with one valence electron. Attention has been paid particularly to the magnetic sublevel population of the residual ions, as described in terms of alignment parameters. Simple method, based on an independent particle model, which takes into account the Pauli principle, is proposed for evaluating the alignment of the excited ionic states. By making use of this method, detailed calculations are performed for electron capture into (initially) hydrogen-like and lithium-like europium, gold and uranium ions, and are compared with the results of the multiconfiguration Dirac-Fock approach.As seen from the calculations and from the comparison with available experimental results, the independent particle model provides a good estimate for the alignment parameters of few-electron heavy ions. Therefore, our simple model may help to understand the basic properties of the X-ray emission from heavy, few-electron ions without the need for invoking sophisticated MCDF calculations.

Two-step mechanisms in ionization-excitation of He studied by binary(e,2e)experiments and second-Born-approximation calculations

An electron momentum spectroscopy study on ionization-excitation processes of He is reported. The symmetric noncoplanar $(e,2e)$ cross sections for transitions to excited ion states have been measured relative to that to the ground ion state at impact energies of 1240 and $4260\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The experimental results exhibit a marked dependence on the impact energy. This provides strong evidence that higher-order effects are involved. Second-Born-approximation calculations are performed and their results are compared with the experimental ones. It is shown that the two-step mechanisms play crucial roles in the ionization-excitation processes.

Two-loop QED corrections in few-electron ions

Results of a calculation valid to all orders in the nuclear-strength parameter Zα are presented for the two-loop Lamb shift, notably for the two-loop self-energy correction, for the ground and first excited states of ions with the nuclear charge numbers Z = 60–100. A detailed comparison of the all-order calculation with earlier investigations based on an expansion in the parameter Zα is given. The calculation removes the largest theoretical uncertainty for the 2pj–2s transition energies in heavy Li-like ions and is important for interpretation of experimental data.PACS Nos.: 31.30.Jv, 31.30.–i, 31.10.+z

Photoinduced Dynamics of Hydrated Adenine Clusters

We studied the photoinduced dynamics of hydrated adenine clusters by multiphoton ionization techniques. The majority of the hydrated adenine monomers are found to experience dissociative ionization, where the adenine monomer ions are produced due to the fragmentation of the water solvents by three-photon process. Due to fast internal conversion from the electronic states reached by the first photon, the fragmentation takes place in the vibrationally excited electronic ground state and in the vibrationally excited ionic states. Thus, the abundance of the hydrated adenine monomer ion depends on the excitation photon energy, possibly because the lifetime of the intermediate states is different and an internal conversion competes with direct ionization. In addition, a significant amount of protonated adenine monomer is observed. This indicates that the proton transfer is followed by the fragmentation in the hydrated adenine clusters. The abundance of the protonated adenine monomer also depends on the excitation photon energy mainly due to the ionization efficiency of the parent species.

Measurement of the fraction of reabsorbed light in an Er3+-doped glass

We report on an original continuous holographic grating technique to quantify the excitation transport within the excited states of erbium ions. We measure a very long range effect well beyond the μm distance which is attributed to radiation trapping. We demonstrate that 30% of the emitted light is reabsorbed inside the sample due to total internal reflections (TIR). The effect of reabsorption is totally removed when TIR are reduced by refractive index matching of the surroundings of the sample.

Quantum and classical transport of excited states of ions

We study the dynamics of the internal state of fast ions traversing amorphous foils using an approach that incorporates the interaction with the radiation field and the complex array of collisions with particles in the solid within the framework of system–reservoir interactions. We have developed from first principles a quantum master equation describing the dynamics of the internal states, including both sinks (electron loss) and sources (electron capture). We illustrate signatures of coherences in experimental findings and discuss the applicability of the quantum and classical linear limits.

Routes to multiphoton double ionization in combined extreme ultraviolet and infrared laser pulses

Xenon multiphoton double ionization pathways are studied in a reaction microscope using a pump-probe arrangement of extreme ultraviolet high harmonic and infrared laser radiation. The momentum of photoelectrons is recorded in coincidence with singly or doubly charged ions. Among all possible routes to multiphoton double ionization, sequential processes using ionic excited states as intermediate steps are clearly identified.