Isomer shifts and changes of the nuclear charge radii in99Ru and101Ru

The recoilless nuclear gamma resonance of the 127 keV γ-rays of¹⁰¹Ru was observed in ruthenium metal, RuO₂ and [Ru(NH₃)₄(HSO₃)₂]. By comparison of the isomer shifts observed in these materials for the 127 keV absorption line with the corresponding shifts of the 90keV γ-rays of⁹⁹Ru one obtains δ〈r ²〉 [127 keV]/ δ〈r ²〉 [90 keV]=1.78±0.26 for the ratio of the changes of the mean square nuclear charge radii between the first excited and the ground states in these nuclei. An estimate of electron density differences based on free-ion relativistic self-consistent field calculations yields δ〈r ²〉[90keV]≈+1.4·10^?3 for⁹⁹Ru and δ〈r ²〉/〈r ²〉 [127 keV]≈+2.4·10^?3 for the¹⁰¹Ru case. These results are discussed in terms of the core excitation model.     

Measurement of the Σ−→ne −¯v and Σ−→ nμ−¯v rates

The recoilless nuclear resonance absorption of the 90 keVγ-rays of⁹⁹Ru was observed in a variety of chemical compounds of ruthenium in the oxidation states +2 through +8 at 4.2 ° K. For most of the compounds isomer shifts increasing monotonically with the oxidation state of ruthenium were found. This behaviour, which may essentially be attributed to the decreasing number of 4d electrons, and the few exceptions from it are discussed qualitatively on the basis of the molecular orbital theory.     

Estimation of the value of ΔR/R for121Sb nucleus by means of Mössbauer spectroscopy and molecular orbital calculation

The¹²¹Sb Mössbauer spectra of rapidly frozen solutions of antimony compounds were observed. The isomer shifts were compared with the electron density at the antimony nucleus calculated with the ab initio molecular orbital method. A value ΔR/R=?(11±2)×10^?4 was derived for the 37.15 keV M1 transition of¹²¹Sb.     

Isotope shift in Ni I and changes in mean-square nuclear charge radii of the stable Ni isotopes

The isotope shift in the Ni I spectrum was studied in 17 lines for all stable isotopes by means of a photoelectric recording Fabry-Perot spectrometer with digital data processing. The measured isotope shifts were separated into mass shift and field shift by comparing the optical isotope shift with model-independent δ〈r ²〉 values derived from a combined elastic electron scattering and muonic x-ray data analysis. The ratios of the observed field shifts in different types of transitions could be explained quantitatively by Hartree-Fock calculations. The relative changes in mean-square nuclear charge radii were found to be: [58, 60] 1.293(15); [60, 62]1; [62, 64] 0.641(16); [60, 61] 0.382(9). The absolute value δ〈r ²〉^60,62=0.170(35) fm² was derived using fine structure as well as hyperfine structure data for the determination of the change in the electron charge density at the nucleus in 4s-4p transitions.     

Calibration of the isomer shift of121Sb and119Sn by means of Mössbauer spectroscopy and molecular orbital calculation

The relationship between the isomer shifts in Mössbauer spectroscopy and the electron contact densities has been investigated for several antimony and tin compounds. Mössbauer spectra for¹²¹Sb in rapidly frozen solutions of antimony compounds were measured. The isomer shifts are compared with the valence electron densities at the antimony nucleus calculated with theab initio molecular orbital method. The relative difference of the nuclear charge radius ΔR/R could be obtained as ΔR/R =?(10.2±1.0)×10^?4 for the 37.15 keV M1 transition of¹²¹Sb. Further, some computations of the electron density at the tin nucleus for several tin compounds were performed. By comparing the valence electron contact densities with isomer shifts, which had been reported for several tin compounds in rare-gas matrix states, the value of ΔR/R for 23.87 keV M1 transition in¹¹⁹Sn was estimated to be (1.57±0.03)×10^?4.     

EPR studies of rhodium in LiH and LiD single crystals

EPR studies of rhodium in LiD and LiH single crystals reveal an axial rhodium complex with the unpaired electron in a 4d_x²?y² molecular orbital and with 5% of the spin density transferred to the planar ligands.     

Spectroscopic and quantum-chemical investigations of chloro-bis-bipyridyl complexes of ruthenium(II) with 4-substituted pyridine ligands

The luminescence spectra of cis-[Ru(bpy)₂(L)Cl]⁺ (bpy is 2,2′-bipyridyl; L is pyrazine, pyridine, 4-amino-pyridine, 4-picolin, isonicotinamide, 4-cyanopyridine, or 4,4′bipyridyl) complexes are studied in alcoholic (4: 1 EtOH-MeOH) solutions at 77 K. A linear correlation is found between the energy of the lowest electronically excited metal-to-ligand charge transfer (³MLCT) state d _π(Ru) → π* (bpy) and the parameter pK _a of the free 4-substituted pyridines and pyrazine used as ligands L. The [B3LYP/6-31G + LanL2DZ(Ru)] hybrid method of the density functional theory is used to optimize the geometry of complexes and calculate their electronic structure and the charge distribution on the atoms of the nearest environment of the ruthenium ion. It is shown that there exists a linear unambiguous correlation between the negative charge on the nitrogen atom (qN ^L) of ligands L coordinated in the complex and the parameters pK _a of free ligands. The calculated energies of ³MLCT excited states almost linearly (correlation coefficient 0.958) depend on the charge qN ^L, which completely agrees with experimental data.     

Calibration of the isomer shift of the 14.4?keV transition?of? 57 Fe

With the aim of calibrating Mössbauer spectroscopic measurements, the electron contact density was calculated on the Fe nuclear position in various iron compounds. The full-potential augmented-plane waves plus local orbitals (APW+lo) method within the local-density approximation was used, considering different approximations for the exchange and correlation potential. By comparison with experimental ⁵⁷Fe Mössbauer data, the calibration constant ?? relating measured isomer shifts to the electron contact density was derived. An isomer shift calibration constant ???=???0.25₁ a.u.³ mm s^???1 has been obtained.     

Chemistry of a novel zerovalent ruthenium π-acidic alkene complex,Ru (η6-1,3,5-cyclooctatriene)(η2-dimethyl fumarate)2

A novel zerovalent ruthenium complex with a π-acidic ligand, Ru(η⁶-cyclooctatriene)(η²-dimethyl fumarate)₂ (1), was prepared from Ru(η⁴-cyclooctadiene)(η⁶-cyclooctatriene) [Ru(cod)(cot)]. Complex 1 or Ru(cod)(cot) catalyzes various new carbon-carbon bond-forming reactions that include the [2 + 2] cycloaddition of alkenes and alkynes via ruthenacycles, the creation of a new hydrocarbon, pentacyclo[6.6.0.0^2,6.0^3,13.0^10,14]tetradeca-4,11-diene [PCTD], by dimerization of 2,5-norbornadiene via C-C bond cleavage, and the codimerization of alkynes and/or alkenes. Complex 1 was shown to be an excellent mother complex for various zerovalent ruthenium complexes. Complex 1 reacts with amines, phosphines or water to give new zerovalent ruthenium complexes with the ligands. The resulting aqua complexes have a water ligand with an oxygen atom that is a chiral center, i.e., ruthenium complexes with a ‘chiral water’ ligand were prepared and fully characterized.     

Stark broadening and shift of some isolated spectral lines of singly ionised earth alkaline metals

Using aZ pinch discharge as a plasma source the profiles and shifts of some prominent ion lines of earth alkaline metals were measured and compared with Stark broadening theories and other experimental results. An electron density of 3.1 to 10.3×10¹⁶ cm^?3 was determined by the laser interferometry, while the electron temperature in the range 25100 to 34800 °K were measured from relative intensities of spectral lines. Comparison of reported experimental shifts and widths with the theories both semi-classical and quantum mechanical shows good agreement. It was also found that Griem's semi-empirical formula is useful and accurate for line widths evaluation.     

Isomerieverschiebungen der 81 keV γ-Linie des133Cs

Isomer shifts of the 81.0 keVγ-transition in¹³³Cs have been measured by the Mössbauer technique for eight ionic Cs compounds, and for the intermetallic compound CsBi₂. The source was¹³³Ba in CaF₂. The shifts, relative to CsCl, range from ?1.4 · 10^?8 eV for CsNO₃ to +1.6 · 10^?8 eV for CsBi₂. The difference in electron density at the Cs nucleus between CsBi₂ and CsNO₃ is discussed using chemical bonding arguments. For the Cs halides, this difference is estimated from the overlap of outer electron shells in the lattices. A relative change of the mean square charge radiusδ〈r ²〉/〈r ²〉=+2 · 10^?4 is derived.     

Relation of contact densities with Mössbauer isomer shifts for 35.46 keV M1 transition of125Te

The internal conversion electron and Mössbauer isomer shifts associated with the 35.46 keV M1 transition of¹²⁵Te were observed for different metal samples into which radioactive¹²⁵I as probe atoms were introduced by means of ion-implantation. From the correlation between the Mössbauer isomer shifts and intensity ratios of O shell to N_I shell conversion electrons, a relation between 5s-electron contact densityp _5s(0) in a.u. and isomer shift δ in mm/s was deduced to bep _5s(0)=106+30.3 δ±4.3[(δ?0.30)²+0.069]^1/2, where δ was measured relative to ZnTe in mm/s. The change of the nuclear charge radius in the 35.46 keV M1 transition of¹²⁵Te was found to be ΔR/R=(0.85±0.12)×10^?4 (corresponding to Δ<r ²>=(3.7±0.5)×10^?3 fm²) when a theoretical 4s-electron contact density of 928 a.u. was used.     

Stark broadening and shift of fluorine I lines

Stark widths and shifts of some prominent F I spectral lines have been determined experimentally in aZ-pinch plasma in dichlorodifluoromethane on a shot-to-shot basis. The electron density was determined by the laser interferometry while the electron temperature was measured from relative intensities of Cl II lines. Temperatures were in the range 19100–36200 °K; electron densities varied from 0.71 to 1.43×10¹⁷cm^?3. Measured F I linewidths and shifts are compared with theoretical results computed by Griem and it is shown that a) experimental widths are systematically smaller and the degree of discrepancy increases with temperature, b) line shifts are also smaller than theoretical with exception of multiplets 5 and 6 with the shifts of opposite sign than theoretically predicted, c) experimental shift-to-width ratios decrease with the temperature but less than theoretically expected. Attention is drawn in general, to the systematic discrepancy between experimental results for neutral atom lines and the theory. The magnitude of this disagreement is related to the relative position of the energy levels of spectral line to the ionisation limit.     

Excitation of He+ in a hollow cathode arc discharge

Population densities of the excited He(II) levels i=4 to i=10 in hollow cathode arc discharge have been determined and compared with those calculated from a collisional-radiative model. In the experiment the electron temperature was about 2x10⁵K and the electron density about 3x10¹⁹ m^-3. The observed population densities agree within 50% with those calculated by Drawin and Emard, but differ by a factor 4–6 from the ones found by McWhirter and Hearn. The results of the present experiment suggest that near the threshold energies the cross sections for electronic excitation of He⁺ levels from the He⁺ ground state are half those expected from the calculations of Burgess. We conclude that Drawin and Emard's calculations should preferably be employed for the determination of the electron density and the electron temperature from observed population densities.     

Evidence for localized excitations in MgO from electron energy-loss spectroscopy

The excited electronic states in the ionic crystal MgO have been studied by electron energy-loss spectroscopy. Structure observed above the thresholds for excitation from the Mg 2p, 2s and 1s core levels shows the final states to be predominantly excitonic levels of the Mg²⁺ ion. Comparison with the known states of the Mg²⁺ free ion indicates that solid-state shifts and splittings are small.     

Isomer-shift analogue in neutron resonances

For the first time, the recently predicted chemical shift of neutron resonances, to be regarded as an analogue to the Mössbauer isomer shift, has been experimentally observed studying the 6.67 eV resonance of ²³⁸U. The experimental shifts were determined by a chi-square fitting technique from the time-of-flight transmission spectra of metallic uranium and four uranium compounds measured at the Dubna IBR-30 pulsed reactor. A computational method has been applied to estimate, and compensate for, the influence of the crystal-lattice vibrations on the experimental values thus obtained. The electron density differences at the nucleus have been calculated for the various sample pairs using available data on chemical X-ray shifts in uranium compounds, on Mössbauer isomer shifts in isovalent neptunium compounds and on free-ion electron densities. The resonance shift results lead to the conclusion that the mean-square charge radius of ²³⁸U diminishes by 1.7_?0.8^+1.2 fm² upon capturing the resonance neutron.     

Excited states dynamics under high pressure in lanthanide-doped solids

Emission related to rare earth ions in solids takes place usually due to 4fⁿ→4fⁿ and 4fⁿ⁻¹5d¹→4fⁿ internal transitions. In the case of band to band excitation the effective energy transfer from the host to optically active impurity is required. Among other processes one of the possibilities is capturing of the electron at the excited state and the hole at the ground state of impurity.The latest results on high pressure investigations of luminescence related to Pr³⁺ and Eu²⁺ in different lattices are briefly reviewed. The influence of pressure on anomalous luminescence and 4fⁿ⁻¹5d¹→4fⁿ luminescence in BaSrF₂:Eu²⁺ and LiBaF₃:Eu²⁺ systems and Pr³⁺ 4fⁿ→4fⁿ emission quenching is presented and discussed. A theoretical model describing the impurity-trapped exciton as a system where a hole is localized at the impurity and an electron is captured by Coulomb potential at Rydberg-like states is developed. The results show the importance of local lattice relaxation for the creation of stable impurity-trapped exciton states. The ligands shifts create a potential barrier that controls the effect of mixing between the Rydberg-like electron and localized electron wave functions.     

Two-soliton and three-soliton interactions of electron acoustic waves in quantum plasma

The overtaking collision between electron acoustic multisolitons in an unmagnetized quantum plasma consisting of ions, and both hot and cold electrons has been investigated. The Hirota bilinear method is employed to study phase shifts and trajectories during the overtaking collision of multisolitons. It is observed that phase shifts are significantly affected by the quantum parameter H. The phase shifts are proportional to B^1/3 (dispersion coefficient) and are functions of their respective amplitudes. It is also seen that the soliton structure occurs only if H < 2.     

Transient photocurrent saturation and deep trapping in hydrogenated amorphous silicon

The transient photocurrent following laser impulse excitation has been measured as a function of laser excitation density for several samples of undoped hydrogenated amorphous silicon (a-Si:H). A feature is observed in these data which is interpreted as originating from complete saturation of the occupancy of deep electron traps. The trap density is estimated from this feature and compared to the neutral dangling bond defect density obtained from electron spin resonance; both measurements are of the same magnitude. Estimates of the density of states, g¹(E), using the measured trap density are also presented.     

Absorption edge shift in ZnO thin films at high carrier densities

The optical absorption edge has been measured as a function of carrier concentration for thin films of zinc oxide prepared by organometallic chemical vapour deposition and reactive R.F. magnetron sputtering. Large shifts of the absorption edge have been observed which are only a function of the carrier concentration. Below n = 3 × 10¹⁹ cm^-3 the shifts are well described by the Burstein-Moss model. For carrier concentrations between 3–5 ×10¹⁹cm^-3, the shift decreases very rapidly, finally increasing again with further increases in the carrier density. These effects are consistent with a merging of the donor band with the conduction band following a semiconductor-metal transition.