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Pressure Effect on the Structural Transition and Suppression of the High-Spin State in the Triple-Layer T;#8242;-La[subscript 4]Ni[subscript 3]O[subscript 8]
We report a comprehensive high-pressure study on the triple-layer T{prime}-La{sub 4}Ni{sub 3}O{sub 8} with a suite of experimental probes, including structure determination, magnetic, and transport properties up to 50 GPa. Consistent with a recent ab inito calculation, application of hydrostatic pressure suppresses an insulator-metal spin-state transition at P{sub c} {approx} 6 GPa. However, a low-spin metallic phase does not emerge after the high-spin state is suppressed to the lowest temperature. For P > 20 GPa, the ambient T{prime} structure transforms gradually to a T-type structure, which involves a structural reconstruction from fluorite La-O{sub 2}-La blocks under low pressures to rock-salt LaO-LaO blocks under high pressures. Absence of the metallic phase under pressure has been discussed in terms of local displacements of O{sup 2-} ions in the fluorite block under pressure before a global T phase is established.
Shape evolution at high spin states in Kr and Br isotopes
The high spin states in A = 75, Kr and Br isotopes have been populated via fusion-evaporation reaction at an incident beam energy of 90 MeV. The de-exciting γ-rays were detected utilizing the Indian National Gamma Array (INGA). Lifetime of these excited high spin states were determined by Doppler-shift attenuation method. Experimental results obtained from lifetime measurement are interpreted in the frame work of projected shell-model to get better insight into the evolution of collectivity. Comparison of the calculations of the model with transitional quadrupole moments Q{sub t} of the positive and negative parity bands firmly established their configurations.
Dipole bands in high spin states of {sub 57}{sup 135}La{sub 78}
High spin states of {sup 135}La have been investigated using the reaction {sup 128}Te({sup 11}B,4n){sup 135}La at a beam energy of 50.5 MeV. Two negative parity dipole bands (ΔI = 1) have been established. Crossover E2 transitions have been observed for the first time in one of the dipole bands. For the Tilted Axis Cranking (TAC) calculations, a three-quasiparticle (3qp) configuration π(h{sub 11/2}){sup 1}⊗ν(h{sub 11/2}){sup −2} and a five-quasiparticle (5qp) configuration π(h{sub 11/2}){sup 1}(g{sub 7/2}/d{sub 5/2}){sup 2}⊗ν(h{sub 11/2}){sup −2} have been taken for the two negative parity dipole bands. The comparison of experimental observables with TAC calculations supports the configuration assignments for both the dipole bands.
High-spin states in 60 Cu and implications for states in the mirror nucleus 60 Ga
High-spin states in 60 Cu are investigated on the basis of reaction-channel-selected 𝛾-ray spectroscopy. Data stem from three experiments that used the same fusion-evaporation reaction at similar beam energies. The Gammasphere 𝛾-ray spectrometer was combined with the Microball CsI(Tl) detector array and sets of liquid-scintillator neutron detectors which allowed us to identify and tag on evaporated light charged particles and neutrons, respectively. A level scheme is proposed which comprises more than 300 𝛾-ray transitions connecting more than 100 excited states. Predictions from cranked Nilsson-Strutinsky calculations describe the observed high-spin collective structures in 60 Cu. Predictions of shell-model calculations are probed with a suite of low- to medium-spin states of both parities. Taking into account isospin-symmetry-breaking terms in these calculations, a case study of the yrast line of the weakly bound mirror nucleus 60 Ga is presented.
Understanding the Existence of a Na 2 Dimer in a High-Spin State
The recent observation of a high-spin Na 2 dimer formed on the surface of liquid helium nanodroplets raises some fundamental questions, as the ground state of Na 2 is known to have zero spin. Is it protected against spontaneous dissociation? What is its binding energy and interatomic distance? Is it stable at a higher temperature? Using calculations based on density functional theory (with and without long-range interaction) and coupled cluster methods, CCSD(T), we show that the bonding in the high-spin Na 2 dimer is governed by van der Waals interaction with binding energy (bond length) varying between −0.030 eV (5.108 Å) and −0.192 eV (4.231 Å), depending on the computational method used. Thus, the experimental method used by Kresin and coworkers can be very useful to study larger metastable high-spin clusters such as Li 4 which was predicted in 1985 to have a tetrahedral structure carrying a magnetic moment of 2 μ B , while its ground state is planar and nonmagnetic.
Direct observation of high-spin states in manganese dimer and trimer cations by x-ray magnetic circular dichroism spectroscopy in an ion trap
The electronic structure and magnetic moments of free Mn{sub 2}{sup +} and Mn{sub 3}{sup +} are characterized by 2p x-ray absorption and x-ray magnetic circular dichroism spectroscopy in a cryogenic ion trap that is coupled to a synchrotron radiation beamline. Our results directly show that localized magnetic moments of 5 μ{sub B} are created by 3d{sup 5}({sup 6}S) states at each ionic core, which are coupled ferromagnetically to form molecular high-spin states via indirect exchange that is mediated in both cases by a delocalized valence electron in a singly occupied 4s derived antibonding molecular orbital with an unpaired spin. This leads to total magnetic moments of 11 μ{sub B} for Mn{sub 2}{sup +} and 16 μ{sub B} for Mn{sub 3}{sup +}, with no contribution of orbital angular momentum.
An improved numerical method to compute neutron/gamma deexcitation cascades starting from a high spin state
Numerous nuclear processes involve the deexcitation of a compound nucleus through the emission of several neutrons, gamma-rays and/or conversion electrons. The characteristics of such a deexcitation are commonly derived from a total statistical framework often called “Hauser–Feshbach” method. In this work, we highlight a numerical limitation of this kind of method in the case of the deexcitation of a high spin initial state. To circumvent this issue, an improved technique called the Fluctuating Structure Properties (FSP) method is presented. Two FSP algorithms are derived and benchmarked on the calculation of the total radiative width for a thermal neutron capture on 238 U. We compare the standard method with these FSP algorithms for the prediction of particle multiplicities in the deexcitation of a high spin level of 143 Ba. The gamma multiplicity turns out to be very sensitive to the numerical method. The bias between the two techniques can reach 1.5 γγ/cascade. Lastly, the uncertainty of these calculations coming from the lack of knowledge on nuclear structure is estimated via the FSP method.
Coexistence of low and high spin states in La 18 Co 28 Pb 3
The electronic structure and magnetic properties of a newly predicted stable ternary compound La 18 Co 28 Pb 3 are studied using electronic structure analysis. The ground state of this compound is ferromagnetic, with three positions of nonequivalent magnetic Co atoms. A strong dependence of magnetic properties on volume shows that this system is situated near the point of magnetic instability. The coexistence of high- and low-spin ferromagnetic states as a function of volume near equilibrium was discovered. A corresponding spin tunneling splitting was estimated. The stability of the theoretically predicted magnetic ground state was tested by varying the Hubbard parameter. The thermal spin fluctuations were added to estimate the paramagnetic moment and a Curie temperature. Finally, the necessity of experimental verification of the obtained results is emphasized.
Dynamic Jahn–Teller Effect in the Metastable High-Spin State of Solvated [Fe(terpy) 2 ] 2+
Characterizing structural distortions in the metastable spin states of d4- 11 d7 transition metal ion complexes is crucial to understand the nature of their bistability 12 and eventually control their switching dynamics. In particular, the impact of the Jahn- 13 Teller effect needs to be assessed for any electronic configuration that could be 14 effectively degenerate, as in e.g. the high-spin (HS) manifold of highly symmetric 15 homoleptic FeII complexes. However, capturing its manifestations remains challenging 16 since crystallization generally alters the molecular conformations and their 17 interconversion. With the rapid progress of ultrafast X-ray absorption spectroscopy, it 18 is now possible to collect data with unprecedented signal-to-noise ratio, opening up for 19 detailed structural characterization of transient species in the homogeneous solution phase. By combining the analysis of 20 picosecond X-ray absorption spectra with DFT simulations, the structure of the photoinduced HS state is elucidated for solvated 21 [Fe(terpy)2]2+ (terpy = 2,2':6',2''-terpyridine). This species can be viewed as the average 5B structure in D2 symmetry that 22 originates from a dynamic Jahn-Teller effect in the HS manifold. These results evidence the active role played by this particular 23 instance of vibronic coupling in the formation of the HS state for this benchmark molecule. Ultimately, correlating the interplay 24 between intramolecular and intermolecular degrees of freedom to conformational strain and distortions in real time should 25 contribute to the development of advanced functionalities in transition metal ion complexes.
High-Spin State of a Ferrocene Electron Donor Revealed by Optical and X-ray Transient Absorption Spectroscopy
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Mechanistic implications of excited high-spin states, spin–spin coupling, and differential [2Fe–2S] + cluster temperature relaxations in the electron-bifurcating NfnABC from Thermococcus sibiricus
Electron bifurcation (EB) is a mechanism of biological energy transduction in which multiple oxidation–reduction (redox) reactions are thermodynamically coupled within a single enzyme, enabling the enzyme to harness the excess free energy from an exergonic process to drive an endergonic process. Because of this unprecedented chemistry, there is interest to translate EB principles to artificial and bioengineered systems, but a hurdle is that knowledge pertaining to the fundamental design principles of EB enzymes remains scarce. Here, we investigated the fundamental physical and electronic properties of electron transfer sites in a spectroscopically uncharacterized member of the BfuABC family of EB enzymes, the NADH-dependent reduced-ferredoxin:NADP + oxidoreductase from Thermococcus sibiricus (Tsi NfnABC). Cryo-EM structures of Tsi NfnABC previously demonstrated that it contains twelve redox cofactors: two flavins (one FAD and one FMN), eight [4Fe–4S] clusters, and two [2Fe–2S] clusters. The FMN, one [4Fe–4S] cluster, and one [2Fe–2S] cluster comprise the bifurcating active site termed the electron-bifurcating flavobicluster (BF-FBC), which is found in all BfuABC family members. By using electron paramagnetic resonance spectroscopy, we identified spectral signatures originating from interactions between the FMN radical and [4Fe–4S] + cluster in the BF-FBC and observed temperature dependent behavior of the BF-FBC's [2Fe–2S] + cluster indicative of moderately slow spin–lattice relaxation. Additionally, we uncovered numerous spectral features corresponding to half-integer, S > ½ spin states of [4Fe–4S] + clusters, including one attributable to the consequences of lysine-ligation of a [4Fe–4S] cluster unique to NfnABC. We contextualize these findings to electron transfer theory and NfnABC's structure. Our insights further the understanding of how enzymes are designed to exert control over electron transfer to conduct thermodynamically challenging reactions.
Low-, medium-, and high-spin states in the N = Z + 1 nucleus Ga 63
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Reinvestigation of high spin states and proposed octupole correlations in Ce 147
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Doubly magic Pb 208 : High-spin states, isomers, and E 3 collectivity in the yrast decay
Yrast and near-yrast levels up to spin values in excess of I = 30h have been delineated in the doubly-magic 208 Pb nucleus following deep-inelastic reactions involving 208 Pb targets and, mostly, 430-MeV 48 Ca and 1440-MeV 208 Pb beams. The level scheme was established up to an excitation energy of 16.4 MeV, based on multi-fold γ-ray coincidence relationships measured with the Gammasphere array. Below the well-known, 0.5-μs 10 + isomer, ten new transitions were added to earlier work. The delineation of the higher parts of the level sequence benefited from analyses involving a number of prompt- and delayed-coincidence conditions. Three new isomeric states were established along the yrast line with I π = 20 - (10342 keV), 23 + (11361 keV), and 28 - (13675 keV), and respective half-lives of 22(3), 12.7(2), and 60(6) ns. Gamma transitions were also identified preceding in time the 28 - isomer, however, only a few could be placed in the level scheme and no firm spin-parity quantum numbers could be proposed. In contrast, for most states below this 28 - isomer, firm spin-parity values were assigned, based on total electron-conversion coefficients, deduced for low-energy (<500 keV) transitions from γ-intensity balances, and on measured γ-ray angular distributions. The latter also enabled the quantitative determination of mixing ratios. The transition probabilities extracted for all isomeric transitions in 208 Pb have been reviewed and discussed in terms of the intrinsic structure of the initial and final levels involved. Particular emphasis was placed on the many observed E3 transitions as they often exhibit significant enhancements in strength (of the order of tens of W.u.) comparable to the one seen for the neutron j 15/2 →g 9/2 E3 transition in 209 Pb. In this context, the enhancement of the 725-keV E3 transition (56 W.u.) associated with the decay of the highest-lying 28 - isomer observed in this work remains particularly challenging to explain. Large-scale shell-model calculations were performed with two approaches, a first one where the 1, 2, and 3 particle-hole excitations do not mix with one another, and another more complex one, in which such mixing takes place. We compared the calculated levels with the data and a general agreement is observed for most of the 208 Pb level scheme. At the highest spins and energies, however, the 2 correspondence between theory and experiment is less satisfactory and the experimental yrast line appears to be more regular than the calculated one. This regularity is notable when the level energies are plotted versus the I(I+1) product and the observed, nearly linear, behavior was considered within a simple “rotational” interpretation. Furthermore, within this approximate picture, the extracted moment of inertia suggests that only the 76 valence nucleons participate in the “rotation” and that the 132 Sn spherical core remains inert.
Manipulation of the molecular spin crossover transition of Fe(H 2 B(pz) 2 ) 2 (bipy) by addition of polar molecules
In this paper, the addition of various dipolar molecules is shown to affect the temperature dependence of the spin state occupancy of the much studied spin crossover Fe(II) complex, [Fe{H 2 B(pz) 2 } 2 (bipy)] (pz = pyrazol-1-yl, bipy = 2,2'-bipyridine). Specifically, the addition of benzimidazole results in a re-entrant spin crossover transition, i.e. the spin state starts in the mostly low spin state, then high spin state occupancy increases, and finally the high spin state occupancy decreases with increasing temperature. This behavior contrasts with that observed when the highly polar ρ-benzoquinonemonoimine zwitterion C 6 H 2 ( ... NH 2 ) 2 ( ... O) 2 was mixed with [Fe{H 2 B(pz) 2 } 2 (bipy)], which resulted in locking [Fe{H 2 B(pz) 2 } 2 (bipy)] largely into a low spin state while addition of the ethyl derivative C 6 H 2 ( ... NHC 2 H 5 ) 2 ( ... O) 2 did not appear to perturb the spin crossover transition of [Fe{H 2 B(pz) 2 } 2 (bipy)].