Zikri Altun

Dielectronic Recombination Data for Dynamic Finite-Density Plasmas. I; Goals and Methodology

A programme is outlined for the assembly of a comprehensive dielectronic recombination database within the generalized collisional-radiative (GCR) framework. It is valid for modelling ions of elements in dynamic finite-density plasmas such as occur in transient astrophysical plasmas such as solar flares and in the divertors and high transport regions of magnetic fusion devices. The resolution and precision of the data are tuned to spectral analysis and so are sufficient for prediction of the dielectronic recombination contributions to individual spectral line emissivities. The fundamental data are structured according to the format prescriptions of the Atomic Data and Analysis Structure (ADAS) and the production of relevant GCR derived data for application is described and implemented following ADAS. The requirements on the dielectronic recombination database are reviewed and the new data are placed in context and evaluated with respect to older and more approximate treatments. Illustrative results validate the new high-resolution zero-density dielectronic recombination data in comparison with measurements made in heavy-ion storage rings utilizing an electron cooler. We also exemplify the role of the dielectronic data on GCR coefficient behaviour for some representative light and medium weight elements.

Dielectronic recombination data for dynamic finite-density plasmas - XI : The sodium isoelectronic sequence

Dielectronic recombination (DR) rate coefficients for 22 sodium-like ions, between Mg+ and Xe43+, forming magnesium-like ions have been calculated as part of the assembly of a level-resolved DR database necessary for modelling dynamic finite-density plasmas, within the generalized collisional - radiative framework. Calculations have been performed from both ground and metastable initial states, in both LS - and intermediate coupling, allowing for Delta n = 0 and Delta n = 1 core-excitations from ground and metastable levels. Partial and total DR coefficients have been calculated for Mg+ to Zn19+, as well as Kr25+, Mo31+, and Xe43+. Results for a selection of ions from the sequence are discussed in the paper and compared with existing theoretical and experimental results. A full set of results can be accessed from the Atomic Data and Analysis Structure (ADAS) database or from the Oak Ridge Controlled Fusion Atomic Data Center (http:// www-cfadc.phy.ornl.gov/data_and_codes).

Dielectronic recombination data for dynamic finite-density plasmas VI. The boron isoelectronic sequence

We have calculated dielectronic recombination rate coefficients for 22 ions of the boron isoelectronic sequence, between C+ and Xe49+, within the generalized collisional-radiative framework, as outlined by Badnell et al. (2003). Calculations have been performed from both ground and metastable initial states, in both LS- and intermediate-coupling, allowing for Deltan = 0 and Deltan = 1 core-excitations. Results are presented and discussed for a selection of ions from the sequence. Results which are not presented here can be accessed from the Atomic Data and Analysis Structure (ADAS) database (Summers 2003) or from the Oak Ridge Controlled Fusion Atomic Data Center (http://www-cfadc.phy.ornl.gov). Comparison is made with the results of other existing theoretical calculations.

Dielectronic recombination data for dynamic finite-density plasmas - XIII. The magnesium isoelectronic sequence

We have calculated total and partial final-state level-resolved dielectronic recombination (DR) rate coefficients for the ground and metastable initial levels of 21 Mg-like ions between Al + and Xe 42+ . This is the final part of the assembly of a levelresolved DR database necessary for modelling dynamic finite-density plasmas within the generalized collisional-radiative framework. Calculations have been performed in both LS - and intermediate coupling, allowing for ∆n = 0a nd∆n = 1 core-excitations from ground and metastable levels. Complementary partial and total radiative recombination RR coefficients have been calculated for the same ions viz. Al + through Zn 18+ ,a s well as Kr 24+ ,M o 30+ ,a nd Xe 42+ . Fitting coefficients which describe the total RR and DR rate coefficients (separately) are also presented here. Results for a selection of ions from this sequence are discussed, and compared with existing theoretical and experimental results. A full set of results can be accessed from the Atomic Data and Analysis Structure (ADAS) database or from the Oak Ridge Controlled Fusion Atomic Data Center (http://www-cfadc.phy.ornl.gov/data_and_codes). The complexity of further M-shell sequences, both from the atomic and modelling perspectives, renders this juncture a natural conclusion for the assemblage of the partial database. Further M-shell work, has and will, focus more on total rate coefficients, rather than partials, at least in the medium term.

Complexes with Tunable Intramolecular Ferrocene to Ti(IV) Electronic Transitions: Models for Solid State Fe(II) to Ti(IV) Charge Transfer.

Iron(II)-to-titanium(IV) metal-to-metal-charge transfer (MMCT) is important in the photosensitization of TiO2 by ferrocyanide, charge transfer in solid-state metal-oxide photocatalysts, and has been invoked to explain the blue color of sapphire, blue kyanite, and some lunar material. Herein, a series of complexes with alkynyl linkages between ferrocene (Fc) and Ti(IV) has been prepared and characterized by UV-vis spectroscopy and electrochemistry. Complexes with two ferrocene substituents include Cp2Ti(C2Fc)2, Cp*2Ti(C2Fc)2, and Cp2Ti(C4Fc)2. Complexes with a single ferrocene utilize a titanocene with a trimethylsilyl derivatized Cp ring, (TMS)Cp, and comprise the complexes (TMS)Cp2Ti(C2Fc)(C2R), where R = C6H5, p-C6H4CF3, and CF3. The complexes are compared to Cp2Ti(C2Ph)2, which lacks the second metal. Cyclic voltammetry for all complexes reveals a reversible Ti(IV/III) reduction wave and an Fe(II/III) oxidation that is irreversible for all complexes except (TMS)Cp2Ti(C2Fc)(C2CF3). All of the complexes with both Fc and Ti show an intense absorption (4000 M(-1)cm(-1) < ε < 8000 M(-1)cm(-1)) between 540 and 630 nm that is absent in complexes lacking a ferrocene donor. The energy of the absorption tracks with the difference between the Ti(IV/III) and Fe(III/II) reduction potentials, shifting to lower energy as the difference in potentials decreases. Reorganization energies, λ, have been determined using band shape analysis (2600 cm(-1) < λ < 5300 cm(-1)) and are in the range observed for other donor-acceptor complexes that have a ferrocene donor. Marcus-Hush-type analysis of the electrochemical and spectroscopic data are consistent with the assignment of the low-energy absorption as a MMCT band. TD-DFT analysis also supports this assignment. Solvatochromism is apparent for the MMCT band of all complexes, there being a bathochromic shift upon increasing polarizability of the solvent. The magnitude of the shift is dependent on both the electron density at Ti(IV) and the identity of the linker between the titanocene and the Fc. Complexes with a MMCT are photochemically stable, whereas Cp2Ti(C2Ph)2 rapidly decomposes upon photolysis.

INNER-SHELL PHOTOEXCITATION OF ATOMS AND THEIR IONS : NEUTRAL AND DOUBLY IONIZED SC

The photoionization cross section of ground state Sc2+ is calculated using our augmented many-body-perturbation theory methodology and compared with similar results for neutral Sc. The comparison shows surprising similarities and differences which give new insight into the redistribution of oscillator strength from inner shells in response to the removal of outer-shell electrons.

Photoionization cross section and resonance structure of atomic sulphur

Many-body perturbation theory has been applied to calculate the partial and total photoionization cross sections for neutral sulphur from the first ionization threshold at 10.36 eV to 60 eV. The excitations from the ground state S(3s23p43P), leaving the residual S+ ions in the lowest five LS states (3s23p34S,2D,2P and 3s3p44p,2p), are considered. The results are presented in both the dipole length and velocity forms. The threshold behaviour of the partial photoionization cross sections are found to be dominated by the overlapping autoionizing resonances converging to S+(3s23p34S,2D,2P) and S+(3s3p44P,2P) limits. The excited single-particle states are calculated in an effective single-particle potential which includes, in an approximate way, the effects of the interaction among many final channels. The results are compared with the previous photoionization studies of sulphur.

Photophysical and Analyte Sensing Properties of Cyclometalated Ir(III) Complexes

The synthesis of some heteroleptic, cyclometalated iridium(III) complexes is described. The utility of these [Ir(ppy)2(N-N)]Cl (ppy = 2-phenylpyridine and N-N = substituted bipyridine, biquinoline, or phenanthroline) complexes as luminescence-based sensors is assessed. The emission intensity of an Ir(III) complex featuring the 3,3′-Hndcbpy ligand (Hndcbpy = dicarboxylic acid-2,2′-bipyridine; n = 0,1,2 to indicate deprotonated, mono- and diprotonated species, respectively) is seen to increase in the presence of Pb(II). Insight into the structure and analyte-sensing capability is achieved by X-ray crystallography in conjunction with computational modeling. Complexes incorporating carboxylic acid-functionalized bipyridine and biquinoline as the polypyridyl ligand show pH sensitivity while similar phenanthroline complexes do not.

Enhancement of high-order harmonic generation in the presence of noise

We report on our simulations of the generation of high-order harmonics from atoms driven by an intense femtosecond laser field in the presence of noise. We numerically solve the non-perturbative stochastic time-dependent Schrodinger equation and observe how varying noise levels affect the frequency components of the high harmonic spectrum. Our calculations show that when an optimum amount of noise is present in the driving laser field, roughly a factor of 45 net enhancement can be achieved in high-order harmonic yield, especially, around the cut-off region. We observe that, for a relatively weak noise, the enhancement mechanism is sensitive to the carrier-envelope phase. We also investigate the possibility of generating ultra-short intense attosecond pulses by combining the laser field and noise and observe that a roughly four orders of magnitude enhanced isolated attosecond burst can be generated.

Determination of the recombination rate coefficients for Na-like Si IV forming Mg-like Si III

Aims. Absolute, total recombination rate coefficients for Si iv were determined using the CRYRING heavy-ion storage ring.Calculated rate coefficients were used to estimate recombination into states ...