L x‐ray fluorescence cross‐sections of heavy elements in the atomic region 57 ≤ Z ≤ 71 excited by 17.78 keV photons

L x‐ray fluorescence cross‐sections (σ_Lα, σ_Lβ, and σ_Lγ) were measured with an accuracy of 6% (except for the Lγ x‐ray line around 8%) for La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb and Lu at an excitation energy of 17.78 keV. Relative intensities I_Kβ/I_Kα and I_Lγ/I_Lα were also measured for the same elements. The measured cross‐sections were compared with experimental and theoretical values. Measurements of the emitted x‐rays were performed using an Si(Li) detector. Copyright © 2004 John Wiley & Sons, Ltd.     

Experimental L x‐ray fluorescence cross‐sections for elements with 45 ≤ Z ≤ 50 at 7 keV by synchrotron radiation photoionization

L x‐ray fluorescence cross‐sections for elements with 45 ≤ Z ≤ 50 were measured at 7 keV using synchrotron radiation photoionization. The experimental set‐up provided a linearly polarized monoenergetic photon beam producing a low background and improving the signal‐to‐noise ratio. The data obtained for the L lines, Ll, Lα, Lβ_I, Lβ_II, Lγ_I and Lγ_II, were grouped considering the transition scheme, the energies of the emission lines and the detector resolution. Results for the experimental cross‐sections obtained were compared with theoretical values using two different data tables. In general, it was found that the experimental fluorescence cross‐sections are slightly higher (7–10%) than the theoretically calculated data and in some cases these differences are up to 40%. Copyright © 2005 John Wiley & Sons, Ltd.     

Measurement of L X-ray fluorescence cross sections and relative intensities for some elements in the atomic range 78 ≤ Z ≤ 92

The L X-ray fluorescence cross sections (σ_Ll, σ_Lα, σ_Lη, σ_Lβ, σ_Lβ6, σ_Lβ2,₄, σ_Lβ1,₃, σ_Lβ9,10, σ_Lγ, σ_Lγ1, σ_Lγ2,3, σ_Lγ4 and σ_Lγ5) and relative intensities (I_Lα, I_Ll, I_Lη, I_Lβ, I_Lβ6, I_Lβ2,4, I_Lβ1,3, I_Lβ9,10, I_Lγ, I_Lγ1, I_Lγ2,3, I_Lγ4 and I_Lγ5) for some elements in the atomic range 78 ≤ Z ≤ 92 have been measured at 59.54 keV photons energies from an Am-241 point source. The L X-rays emitted by samples have been counted by a Si(Li) detector. The L X-ray fluorescence cross sections and relative intensities have been also calculated theoretically by using atomic parameters. The measured values have been compared with the theoretical values.     

Three dimensional (Z‐dependence), collective and individual semi‐empirical formulae for L X‐ray production and ionization cross section by protons impact within corrected ECPSSR theory and updated experimental data: a review

In this paper we propose a new three dimensional semi‐empirical formulae for the deduction of L X‐ray production and ionization cross sections by introducing the dependence on the atomic number of the target, noted as ‘Z‐dependence’. The data are also fitted collectively and separately (for each element) by analytical functions to calculate semi‐empirical cross sections. For this purpose, the corrected ECPSSR model (noted as eCPSSR) and the published experimental data of L_α, L_β and L_γ X‐ray production and L₁, L₂ and L₃ ionization cross sections in the period (1950–2014) are combined to calculate the semi‐empirical ones for a wide range of elements by proton impact. The semi‐empirical cross sections (for the three x‐rays lines L_α, L_β, L_γ and the three sub‐shells L₁, L₂, L₃) are then deduced by fitting the available experimental data normalized to their corresponding theoretical values (using the eCPSSR model) giving a better representation of the experimental data for the individual interpolation. At last, a comparison is made between the three semi‐empirical formulae reported in this work. Copyright © 2016 John Wiley & Sons, Ltd.     

Synchrotron radiation induced X‐ray production cross sections of 66Dy at energies across its Li (i = 1–3) subshell absorption edges

The X‐ray production (XRP) cross sections for the ₆₆Dy L_k (k = l, α, η, β_2,6,7,15, β_1,6, β_1,3,4,6, β_2,7,15, γ_1,5, γ₂,₃) emission lines have been measured by tuning the incident synchrotron radiation at energies over the range 7.8–9.2 keV and ~10–370 eV above the respective L_i (i = 1–3) absorption edges. These measurements aim to check the reliability of the independent particle approximation models used to generate the theoretical data sets of different physical parameters required to calculate the XRP cross sections and also investigate the influence of many body effects on the photoionization process. The measured values have been compared with 4 sets of XRP cross sections calculated using the Dirac–Fock model‐based X‐ray emission rates, 2 sets of the L_i (i = 1–3) subshell photoionization cross sections deduced from the self‐consistent Dirac–Hartree–Fock model‐based values and the nonrelativistic Hartree–Fock–Slater model‐based values, and 2 sets of the fluorescence (ω_i) and Coster–Kronig (f_ij) yields. The present measured Lγ_2,3 (originating from decay of the L₁ subshell vacancies) XRP cross sections are found to be significantly higher than different sets of theoretical values, whereas a good agreement is generally observed for the various other XRP cross sections and relative intensities.     

Generation of experimental L x‐ray fluorescence cross‐sections for inter‐elements at inter‐energies EL1 ≤ E ≤ EK (computer program IGELCS)

The experimental values of L x‐ray fluorescence (XRF) cross‐sections are not available for all the elements in the range La–U, at all the photon energies E in the range EL1 ≤ E ≤ EK. To generate L XRF cross‐sections, where experimental measurements are not available, two empirical relations have been developed, one between the L XRF cross‐sections and photon energy and the other between the L XRF cross‐sections and atomic number. For the measured data on L XRF cross‐sections at incident energies between Ll and K edges of an element and the data on L XRF cross‐sections for elements in the range 57 ≤ Z ≤ 92 at an energy value, polynomial fits have been derived. The L XRF cross‐section values generated with the derived empirical relations were found to be in agreement with the experimental values within their experimental uncertainties. Subsequently, a software code IGELCS was developed to interpolate and to generate the cross‐sections at inter‐energies and for inter‐elements in a single computer run. The running of the software requires minimum input data on five elements at five common energies. Copyright © 2003 John Wiley & Sons, Ltd.     

Measurement of L subshell fluorescence yields of some rare earth elements using synchrotron radiation

The L subshell fluorescence yields ω₁, ω₂ and ω₃ of Gd, Tb and Ho have been measured using Indus‐2 synchrotron radiation. The L X‐ray photons generated in the elemental targets by 10 and 11 keV synchrotron radiation have been measured using silicon drift detector that has an energy resolution of 130 eV at 5.9 keV. The measured values of ω₁, ω₂ and ω₃ have been compared with theoretical values, semi‐empirical fitted values and other experimental values. Copyright © 2015 John Wiley & Sons, Ltd.     

Chemical effects of high‐resolution YbLγ4 emission spectra: a possible probe for chemical analysis

An ‘eccentric’ X‐ray emission, YbLγ₄, was measured for Yb metal, Yb₂O₃, YbF₃, β‐YbAlB₄, YbNi₃Al₉, and YbNi₃Ga₉ with a resolution of ~0.9 eV. Peak splitting of the YbLγ₄ line was observed in all the recorded spectra and was attributed to the two components originating from the LS coupling of the Yb5p hole, the Yb5p_1/2 (L_IO_II: Lγ₄′) and Yb5p_3/2 components (L_IO_III: Lγ₄). The spectra were substantially different depending on the chemical environment of Yb. The position of the Lγ₄ + Lγ₄′ band shifts depending on the valence of Yb (v): ~4.4 eV from divalent to trivalent. The Lγ₄ + Lγ₄′ spectra of the mixed valence intermetallics, i.e. YbNi₃Ga₉ (v = 2.59) and β‐YbAlB₄ (v = 2.75), were fairly well reproduced by averaging the spectra of divalent Yb and trivalent YbNi₃Al₉, which suggests the possibility of using the YbLγ₄ emission for determining the valence of Yb intermetallics. In trivalent Yb compounds, the relative intensity of Lγ₄ compared with that of Lγ₄′, as well as the appearance of a high‐energy satellite, was found to be influenced by the ligands around the Yb ions. With the aid of preliminary atomic multiplet and band structure calculations, the differences in the valence band structure and resultant screening effects on the O_II,III^?1 states were determined to be the possible causes for the observed ligand dependence. © 2013 The Authors. X‐ray spectrometry published by John Wiley & Sons, Ltd.     

Cascade Mi (i = 1–5) subshell X‐ray emission at incident photon energies across the Lj (j = 1–3) subshell absorption edges of 66Dy

The total M shell and the M_k (k = ξ, αβ, γ, m) X‐ray production cross sections for ₆₆Dy have been measured at incident photon energies across its L_j (j = 1–3) subshell absorption edge energies, ranging 7.8–9.2 keV. This study aims to investigate the evolution of the probability for cascade decay of L_j subshell vacancies as the tunable incident energy ionizes progressively different ₆₆Dy L_j subshells. The experimental X‐ray production cross sections have been compared with theoretical ones calculated using the nonrelativistic Hartree–Fock–Slater (HFS) model‐based photoionization cross sections; three sets of the X‐ray emission rates, fluorescence and Coster–Kronig yield based on the nonrelativistic Hartree–Slater (NRHS) model, Dirac–Hartree–Slater (DHS) model and Dirac–Fock (DF) model; the L_j (j = 1–3) subshell to the M_i (i = 1–5) subshell vacancy transfer probabilities evaluated in the present work. Presently measured total M shell and the M_αβ X‐ray production cross sections are found to be significantly lower than the theoretical ones evaluated using physical parameters based on the relativistic Dirac–Fock/Dirac–Hartree–Slater model calculations, whereas a much better agreement is observed with respect to the NRHS model‐based calculations; however, the measured X‐ray production cross sections are still systematically lower than the NRHS values.     

2p3/2−13x−1–3x−13d3/2−1 x‐ray satellites in the Lα2 region

The energies and intensities of the various transitions corresponding to the transition scheme 2p_3/2^?13x^?1–3x^?13d_3/2^?1 (i.e. L₃M_x–M_xM₄) were used to compute theoretical Lα₂ satellite spectra in 13 elements in the atomic number range of 62 ≤ Z ≤ 90. The energies were calculated using available HFS data on K–LM and L–MM transition energies. The intensities of all the possible transitions were estimated by considering cross‐sections for the Auger transitions simultaneous to a hole creation and then distributing statistically the total cross‐sections for initial two‐hole states 2p_3/2^?13x^?1 (L₃M_x) amongst various allowed transitions from these initial states to 3x^?13d_3/2^?1 (M_xM₄) final states. Each transition was assumed to give rise to a Gaussian line and the overall spectrum was computed as the sum of these Gaussian curves. The calculated spectra were compared with the available measured Lα satellite spectra. The peaks in the theoretical satellite spectra were identified as the experimentally reported satellites Lα_s, La₁₃, La₁₄ and La₁₇, which lie on the high‐energy side of the Lα₂ dipole line. Copyright © 2005 John Wiley & Sons, Ltd.     

The investigation of K‐shell fluorescence parameters of Zn–Fe alloys with different grain size and microstrain values

It is known that zinc alloys with iron group metals have better corrosion resistance than pure zinc. Owing to the corrosion resistance of these alloys, Zn–Fe coatings are widely used in automotive industry and have excellent mechanical performance. In this work, we investigated the relationship between the changes in the measured X‐ray fluorescence parameters (K_β/K_α, σ_Kα and σ_Kβ) and the changes in the structural parameters such as microstrain or grain size values for Zn–Fe alloys that were prepared with different pH values. To explain these changes, the K_α and K_βX‐ray production cross sections, and the K_β/K_αX‐ray intensity ratio values were calculated by three different ways for the elemental forms of Zn and Fe. The structural parameters, such as microstrain and grain size, were also calculated. We expect that the outer shell electronic distribution affects the structural parameters of the produced Zn–Fe alloys, changing the measured K_α and K_βX‐ray production cross sections, and the K_β/K_αX‐ray intensity ratio values. We also show that Zn–Fe alloy mi nimum microstrain value corresponds to the maximum changes in K_βX‐ray production cross‐section values of Fe and Zn. Copyright © 2017 John Wiley & Sons, Ltd.     

Photoabsorption cross sections for chlorinated methanes and ethanes between 46 and 100 Å

Photoabsorption cross sections for the methanes CCl₄, CCl₃F, CCl₂F₂, CClF₃, CF₄, CHClF₂, CHCl₂F and the ethanes C₂F₆, C₂ClF₅, C₂Cl₂F₄ were measured between 46 and 100 Å. In particular, the 0.2 Å resolution provides some insight into the Cl 2p absorption process. It is noted that the molecular cross section for all 8 Cl-containing gases display an L edge “discontinuity” of 3.55±0.15 Mb per Cl atom. The experimental molecular cross sections are compared with sums of atomic cross sections at 100 Å using both theoretical and empirical atomic values. The sums of theoretical atomic cross sections describe every experimental molecular value to better than 10%. The sums of empirical atomic cross sections describe molecular values to within 2%.     

Measurement of L subshell fluorescence yield ratios of some high Z elements by selective excitation method

The L₁, L₂ and L₃ subshells of Hf, Ta and Re atoms have been excited selectively by using microprobe XRF beam line, Indus‐2, RRCAT, India. The consequent characteristic L X‐ray photons, emitted from the targets due to creations of vacancies in L subshells, are measured using silicon drift detector (X‐123) spectrometer. As the energy of synchrotron radiation increases, the contribution of characteristic L X‐ray intensity increases. The advantage of the increase in the intensity of the characteristic L X‐ray photons with an increase in the energy of synchrotron radiation has been used to determine the L subshell fluorescence yield ratios of Hf, Ta and Re atoms by adopting the selective excitation method. The measured ratios of L subshell fluorescence yield have been compared with theoretical and other experimental values.     

The effect of an external magnetic field on the L subshell X-ray fluorescence cross sections and L subshell fluorescence yields in elements 73 ≤ Z ≤ 92 by 59.54 keV photons

L_i (i = 1, 2 and 3) X-ray fluorescence cross sections for Ta, W, Au, Hg, Tl, Pb, Bi, Th and U have been measured using the 59.54 keV incident photons energy in the external magnetic field of intensity +0.60 T. The values of L_i subshell fluorescence yields (w₁$w_1$, w₂$w_2$ and w₃$w_3$) have been measured for the same elements using the previously measured cross section values and the theoretical L_i subshell photoionisation cross sections, Coster–Kronig transition probabilities and emission rates. It is observed that the measured L_i subshell X-ray fluorescence cross section and L_i subshell fluorescence yield values for B = 0 are in good agreement with the theoretical ones evaluated using L_i subshell fluorescence yield and L_i subshell photoionization cross section. Furthermore, the results show that the atomic parameters such as spectral linewidth, radiation rates, photoionization cross section and fluorescence yield can change when the irradiation is conducted in a magnetic field.     

Complete basis set,hybrid‐DFT study and NBO interpretations of conformational behaviors of trans‐2,3‐ and trans‐2,5‐dihalo‐1,4‐dithianes

The conformational behaviors of trans‐2,3‐dihalo‐1,4‐dithiane [halo = F ( 1 ), Cl ( 2 ), Br ( 3 )] and trans‐2,5‐dihalo‐1,4‐dithiane [halo = F ( 4 ), Cl ( 5 ), Br ( 6 )] have been analyzed by means of complete basis set CBS‐4, hybrid‐density functional theory (B3LYP/6‐311 + G**//B3LYP/6‐311 + G**) based methods, and natural bond orbital (NBO) interpretation. Both methods showed that the axial conformations of compounds 1–5 are more stable than their equatorial conformations but CBS‐4 resulted in an equatorial preference for compound 6 . The Gibbs free energy difference (G_eq?G_ax) values (i.e., ΔG_eq–ax) at 298.15 K and 1 atm between the axial and equatorial conformations decrease from compound 1 to compound 2 but increase from compound 2 to compound 3 . Also, the calculated ΔG_eq–ax values decrease from compound 4 to compound 6 . The NBO analysis of donor–acceptor (LP → σ*) interactions showed that the anomeric effect (AE) increase from compound 1 to compound 3 and also from compound 4 to compound 6 . On the other hand, the calculated dipole moment values between the axial and equatorial conformations [Δ(µ_eq?µ_ax)] decrease from compound 1 to compound 3 . The conflict between the increase of AE and the decrease of Δ(µ_eq?µ_ax) values could explain the variation of the calculated ΔG_eq–ax for compounds 1–3 . The Gibbs free energy difference values between the axial and equatorial conformations (i.e., ΔG_ax–ax and ΔG_eq–eq) of compounds 1 and 4 , 2 and 5 and also 3 and 6 have been calculated. The correlations between the AE, bond orders, pairwise steric exchange energies (PSEE), ΔG_eq–ax, ΔG_ax–ax, ΔG_eq–eq, dipole–dipole interactions, structural parameters, and conformational behaviors of compounds 1–6 have been investigated. Copyright © 2010 John Wiley & Sons, Ltd.     

Li (i = 1, 2, 3) sub‐shell fluorescence yields for 79Au, 80Hg and 81Tl

The L _i (i = 1, 2, 3) sub‐shell x‐ray fluorescence yields (ω _i ) for ₇₉Au, ₈₀Hg and ₈₁Tl were deduced from the measured cross‐sections for the L _i (i = 1, 2, 3) sub‐shell x‐rays following ionization by 59.54 keV γ‐rays (B < E_inc < B_K) and for the L₃ sub‐shell x‐rays following ionization by Rb K x‐rays (B < E_Kα < B, B < E_Kβ < B_K), where B is the K shell/L _i sub‐shell ionization threshold of the target element. An energy‐dispersive x‐ray fluorescence setup, involving photon sources consisting of a ²⁴¹Am annular source in the direct and secondary excitation modes along with RbCl secondary exciter and an Si(Li) detector, was used for the measurements. The measured ω₂ and ω₃ values exhibit good agreement with those based on the relativistic Dirac–Hartree–Slater (RDHS) calculations, while the ω₁ values are found to be higher by ～25%. The present data indicate that the L₁–L₃ Coster–Kronig yield f₁₃ based on the RDHS calculations are overestimated. Copyright © 2004 John Wiley & Sons, Ltd.     

Theoretical design on a new double functional device of 2,2′‐bipyridine‐embedded N‐(9‐pyrenyl methyl)aza‐15‐crown‐5

Theoretical design on a new molecular switch and fluorescent chemosensor double functional device of aza‐crown ether (2,2′‐dipyridine‐embedded N‐(9‐anthraceneyl(pyrenyl)methyl)aza‐15‐crown‐5) was explored. The interactions between ligands and a series of alkaline earth metal cations (Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺) were investigated. The fully optimized geometry structures of the free ligands ( L _1, L ₂) and their metal cation complexes ( L ₁/M²⁺, L ₂/M²⁺) were calculated with the B3LYP/6‐31G(d) method. The natural bond orbital analysis, which is based on optimized geometric structures, was used to explore the interaction of L ₁/M²⁺, L ₂/M²⁺ molecules. The absorption spectra of L _1, L ₂, L ₁/M²⁺, and L ₂/M²⁺, and their excited states were studied by time‐dependent density functional theory. A new type molecular device L ₂(2,2′‐dipyridine‐embedded N‐(9‐pyrenyl methyl)aza‐15‐crown‐5) is designed, which not only has the selectivity for Sr²⁺, and construct allosteric switch, but also has fluorescent sensor performance.     

Calculated polar substituent effects on the stability of 4‐substituted(X) ‐ cub‐1‐yl and ‐bicyclo[2.2.2]oct‐1‐yl cations: a DFT study

The effects of substituents on the stability of 4‐substituted(X) cub‐1‐yl cations ( 2 ), as well as the benchmark 4‐substituted(X) bicyclo[2.2.2]oct‐1‐yl cation systems ( 7 ), for a set of substituents (X = H, NO₂, CN, NC, CF₃, COOH , F, Cl, HO, NH₂, CH₃, SiH₃, Si(CH₃)₃, Li, O^?, and NH) covering a wide range of electronic substituent effects were calculated using the DFT theoretical model at the B3LYP/6‐311 + G(2d,p) level of theory. Linear regression analysis was employed to explore the relationship between the calculated relative hydride affinities (ΔE, kcal/mol) of the appropriate isodesmic reactions for 2 / 7 and polar field/group electronegativity substituent constants (σ_F and σ_χ, respectively). The analysis reveals that the ΔE values of both systems are best described by a combination of both substituent constants. This highlights the distinction between through‐space and through‐bond electronic influences characterized by σ_F and σ_χ, respectively. Copyright © 2010 John Wiley & Sons, Ltd.     

Measurements of Coster–Kronig enhancement factors of some elements in the atomic number range 66 ≤ Z ≤ 72

The Lι, Lα, Lβ and Lγ x‐ray production cross‐sections in four elements with Z ranging from 66 to 72 at seven different energies in the interval 8.265–11.730 keV were measured. Experimental measurements were carried out on a few elemental samples to examine the effect of Coster–Kronig transitions on fluorescence cross‐sections for the L x‐ray line using an Si(Li) detector system with an energy resolution of 160 eV at 5.96 keV x‐ray energy. Absolute values of L x‐ray cross‐sections were calculated with incorporation of the enhancement due to the Coster–Kronig effect for these elements. The measured enhancement factors are smaller than predicted by theory. Copyright © 2003 John Wiley & Sons, Ltd.     

L-SHELL IONIZATION MEASUREMENT OF TUNGSTEN BY ELECTRON IMPACT

L-shell partial production cross sections of L_α^-, L_β^-, L_γ^- rays by electron impact were measured by observing the counts of X-ray from impacted thin tungsten target. Total production cross sections and mean ionization cross sections were deduced from these measured results. The electron beam energy range was from 11 to 36 keV. Tungsten was sputtered onto a carbon backing to reduce bremsstrahlung of the backing. The effect of electrons reflected by the backing has been corrected. Comparison with two theoretical calculations has performed. The experimental results agree rather well with the theoretical predications.