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Here, Anode-free Li-ion batteries could attain new levels of energy density, but challenges remain in controlling deposition and managing degradation. In this issue of Chem, Kwon et al. probe Li metal growth using operando NMR to unravel how cathode materials impact performance and establish criteria for the high-energy/low-cost design tradeoff.
Azulene’s nonradiative decay dynamics and kinetics from its singlet excited-states were studied using mixed-reference spin-flip time-dependent density functional theory (MRSF-TDDFT) combined with trajectory surface-hopping nonadiabatic molecular dynamics (NAMD) and Fermi’s golden rule (FGR) rate theory. The NAMD dynamics reproduce experimental observations that the S 1 → S 0 decay is accelerated and exhibits a crossover from mono- to biexponential kinetics with increasing excess vibrational energy. Minimum-energy-path analyses reveal a continuous S 1 /S 0 conical-intersection seam slightly above the S 1 minimum, providing readily accessible funnels. Time-resolved normal-mode projections reveal selective energy funneling into C–C stretching modes at 1272, 1528, and 1692 cm –1 . Constructive combinations of the latter two modes appear to promote rapid access to the conical-intersection seam, whereas their beating at ∼ 160 fs imposes a natural limit on the decrease of the decay time upon a further increase of excess energies, suggesting that their interference delays the decay. Here, the FGR rate calculation data for the S 1 → S 0 transition reaffirm that the nonradiative decay proceeds mainly near or through the conical intersection, rather than via simple nonadiabatic derivative coupling around the minimum of S 1 . On the other hand, the FGR rates indicate that S 2 decays predominantly to S 0 , as the S 2 –S 1 vibronic coupling is exceptionally weak, which serves as a primary cause for azulene’s characteristic anti-Kasha emission.
The desorption of conventional ligands from the surface of halide perovskite nanocrystals (NCs) often causes their structural instability and the deterioration of the optoelectronic properties. To address this challenge, we present an approach of using a bidentate Lewis base ligand, namely, 1,4-bis(diphenylphosphino)butane (DBPP), for the synthesis of CsPbBr 3 NCs. The phosphine group of DBPP has a strong interaction with PbBr 2 precursor, forming a highly crystalline intermediate complex during the reaction. In the presence of oleic acid, the uncoordinated phosphine group of DBPP is converted into the phosphonium cation, which strongly binds with the surface bromide of the formed CsPbBr 3 NCs through hydrogen bonding. Density functional theory calculations suggest that DBPP can strongly bind to the undercoordinated lead and surface bromide ions of CsPbBr 3 NCs through its unprotonated and protonated phosphine groups, respectively. The robust binding of DBPP with the surface of perovskite NCs helps to preserve their structural integrity under various environmental stresses. Moreover, the electron density and energy levels are regulated in DBPP-capped CsPbBr 3 NCs via the efficient transfer of electrons from the ligands to the NCs, resulting in their improved photocatalytic CO 2 reduction performance. Furthermore, our study highlights the potential of using bidentate ligands to stabilize the surface of perovskite NCs and modulate their optical and electronic properties.
An experiment involving a heavy-ion-induced fusion-evaporation reaction was carried out where high-spin states of 123 Xe were populated in the 80 Se( 48 Ca,5n) 123 Xe reaction at 207 MeV beam energy. Gamma-ray coincidence events were recorded with the Gammasphere Ge detector array. The previously known level scheme was confirmed and enhanced with the addition of five new band structures and several interband transitions. Furthermore, cranked Nilsson-Strutinsky (CNS) calculations were performed and compared with the experimental results in order to assign configurations to the bands.
This article reports on results of an experimental search for ground state shell inversion in the neutron-unbound $\textit{N}$ = 7 isotones 9 He and 10 Li. Two different radioactive ion beams ( 11 Be, E lab = 44 MeV/u and 12 B, E lab = 45 MeV/u) impinging on a beryllium target were used to directly and selectively populate unbound states of a given ℓ in the nuclides of interest. Be( 11 Be, 8 He + $\textit{n}$) and Be( 12 B, 8 He + $\textit{n}$) reactions populated unbound states in 9 He. Fragments and neutrons were detected in coincidence to reconstruct the decay energy of 9 He using invariant mass spectroscopy. Similarly, Be( 11 Be, 9 Li + $\textit{n}$) and Be( 12 B, 9 Li + $\textit{n}$) reactions were used to populate unbound states in 10 Li, and the time-of-flight method was used to determine the relative velocity of the 9 Li fragments and neutrons in coincidence. Various states in both 9 He and 10 Li were observed and characterized. Here, the data indicate possible ground state shell inversion in both cases.
The Z = 50 shell closure, near N = 82, is unique in the sense that it is the only shell closure with the spin-orbit partner orbitals, π g 9 / 2 and π g 7 / 2 , enclosing the magic gap. The interaction of the proton hole/particle in the above-mentioned orbitals with neutrons in the νh 11/2 orbital is an important prerequisite to the understanding of the nuclear structure near N = 82 and the νπ interaction. To explore the structural similarity between the high-spin isomeric states in In ( Z = 49), Sn ( Z = 50), and Sb ( Z = 51) isotopes from a microscopic point of view. In addition, to understand the role of a proton hole or particle in the spin-orbit partner orbitals, π g 9 / 2 and π g 7 / 2 , respectively, with neutron holes in the ν h 11 / 2 orbital on these aforementioned isomers. The fusion and transfer induced fission reaction Be 9 ( U 238 , f ) with 6.2 MeV/u beam energy, using a unique setup consisting of AGATA, VAMOS++, and EXOGAM detectors, was used to populate through the fission process and study the neutron-rich In 119 , 121 isotopes. This setup enabled the prompt-delayed γ -ray spectroscopy of isotopes in the time range of 100 ns – 200 μ s . In the odd- A In 119 , 121 isotopes, indications of a short half-life 19/2 - isomeric state, in addition to the previously known 25/2 + isomeric state, were observed from the present data. Further, new prompt transitions above the 25/2 + isomer in In 121 were identified along with reevaluation of its half-life. The experimental data were compared with the theoretical results obtained in the framework of large-scale shell-model calculations in a restricted model space. Furthermore, the ( π g 9 / 2 ν h 11 / 2 ; I | H ^ | π g 9 / 2 ν h 11 / 2 ; I ) two-body matrix elements of residual interaction were modified to explain the excitation energies and the B ( E 2) transition probabilities in the neutron-rich In isotopes. The (i) decreasing trend of E (29/2 + ) - E (25/2 + ) in odd-In (with dominant configuration π g 9 / 2 - 1 ν h 11 / 2 - 2 and maximum aligned spin of 29/2 + ) and (ii) increasing trend of E (27/2 + ) - E (23/2 + ) in odd-Sb (with dominant configuration π g 7 / 2 + 1 ν h 11 / 2 - 2 and maximum aligned spin of 27/2 + ) with increasing neutron number could be understood as a consequence of hole-hole and particle-hole interactions, respectively.
New ground-state level with spin-parity 1/2 + is established in 109 Mo, 69.8 keV below the previously reported 5/2(+) ground state in this nucleus, based on precise spectroscopy measurements of gamma radiation following spontaneous fission of 248 Cm performed using the Eurogam2 array of anti-Compton spectrometers. Analogous measurement of gamma radiation following spontaneous fission of 252 Cf, performed using the Gammasphere array, confirms the new 1/2 + ground state of 107 Mo, proposed recently and establishes the isomeric character of the 5/2 + first excited state in 107 Mo. Two beta-decaying isomers are suggested in 111 Mo nucleus based on regular energy systematics, supporting previous predictions. Low-energy excitations in Mo isotopes are interpreted and compared to calculations reported in the literature. The results suggest shape transition from prolate to oblate deformation at N >= 67.
The single-particle structure of the N = 27 isotones provides insights into the shell evolution of neutron-rich nuclei from the doubly-magic 48 Ca toward the drip line. 43 S was studied employing the one-neutron knockout reaction from a radioactive 44 S beam. Using a combination of prompt and delayed γ-ray spectroscopy the level structure of 43 S was clarified. Momentum distributions were analyzed and allowed for spin and parity assignments. The deduced spectroscopic factors show that the 44 S ground-state configuration has a strong intruder component. Here, the results were confronted with shell model calculations using two effective interactions. General agreement was found between the calculations, but strong population of states originating from the removal of neutrons from the 2p 3/2 orbital in the experiment indicates that the breakdown of the N = 28 magic number is more rapid than the theoretical calculations suggest.
Transitions in 163 Tb following β decay of 163 Gd were obtained as part of investigations of γ rays emitted following 163 Euβ decay to 163 Gd. In this work, detailed analysis of the low-energy structure of 163 Tb has been carried out with these data to expand previous β-decay studies and reactions studies of levels in 163 Tb. Data were collected at the LeRIBSS station of the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory with an array of four Clover HPGe detectors for γ rays and two plastic scintillators for β detection. The γ rays were identified as belonging to 163 Gd and 163 Tb via mass selection and γ-γ-β, γ-γ, or γ-x-ray coincidence. In total, 38 new γ-ray transitions were observed in 163 Tb from 15 newly identified levels and 12 previously identified levels. Potential energy surface calculations were performed which support a rigid prolate deformation. Previously identified unplaced transitions in 163 Tb have been placed within the level scheme of 163 Tb and additional states and transitions have been identified.
Excited states in 73 , 75 Ni were investigated through the β decay of 73 , 75 Co in an experiment performed at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU). The experimental results extended the level scheme of Ni 73 to 3.2-MeV excitation energy and provided the experimental information on excited states in Ni 75 . The β -delayed neutron branching ratio for Co 73 was obtained. Furthermore, the experimental results are discussed in comparison with shell-model calculations.
Ne 19 is an important isotope in nuclear astrophysics due to its role in both the F 18 ( p , α ) O 15 and O 15 ( α , γ ) Ne 19 reactions in novae and Type I x-ray bursts, respectively. The energy levels of Ne 19 near the α and proton thresholds ( S α = 3529 keV, S p = 6410 keV) correspond to resonances in both of these reactions. Previous measurements to study the structure of Ne 19 have focused on both regions in an effort to constrain these reaction rates. Discrepancies in the energies, spins, and parities for levels in Ne 19 from previous measurements contribute to the reaction-rate uncertainties. Gamma rays from the depopulation of excited states in Ne 19 were measured to reduce the level-energy uncertainties and inconsistencies in previous spin-parity assignments.The F 19 ( He 3 , t ) Ne 19 reaction was used to elucidate the structure of Ne 19 levels up to E x = 6.9 MeV. The reaction products were measured using Gammasphere ORRUBA: Dual Detectors for Experimental Structure Studies—a coupling of the Oak Ridge Rutgers University Barrel Array and Gammasphere at Argonne National Laboratory. Tritons produced in the reaction were measured in coincidence with γ rays from the deexcitation of Ne 19 energy levels. Previously unobserved transitions allowed for discrepancies in the resonance properties relevant to these two reactions to be resolved. In total, 41 transitions from 21 energy levels were measured in Ne 19 , with 21 of those transitions being previously unobserved. Of particular importance, transitions from two 3 / 2 + states with energies of 6423(3) and 6441(3) keV, crucial for accurate estimations of the F 18 ( p , α ) O 15 reaction rate, were found. Energies and spin-parities of important energy levels near the proton and α thresholds were measured and some of the discrepancies in previous measurements were resolved. Overall, measurement of the two near-threshold 3 / 2 + states reduced the calculated upper limit of the F 18 ( p , α ) O 15 reaction rate by factors of 1.5–17 in the nova temperature range.
In the island of inversion, ground states of neutron-rich sd-shell nuclei exhibit strong admixtures of intruder configurations from the fp shell. The nucleus 30 Mg, located at the boundary of the island of inversion, serves as a cornerstone to track the structural evolution as one approaches this region. Spin-parity assignments for excited states in 30 Mg, especially negative-parity levels, have yet to be established. In the present work, the nuclear structure of 30Mg was investigated by in-beam gamma-ray spectroscopy mainly focusing on firm spin-parity determinations. High-intensity rare-isotope beams of 31 Mg, 32 Mg, 34 Si, and 35 P bombarded a Be target to induce nucleon removal reactions populating states in 30 Mg. Gamma rays were detected by the state-of-the-art gamma-ray tracking array GRETINA. For the direct one-neutron removal reaction, final-state exclusive cross sections and parallel momentum distributions were deduced. Multi-nucleon removal reactions from different projectiles were exploited to gain complementary information. With the aid of the parallel momentum distributions, an updated level scheme with revised spin-parity assignments was constructed. Spectroscopic factors associated with each state were also deduced. Results were confronted with large-scale shell-model calculations using two different effective interactions, showing excellent agreement with the present level scheme. Furthermore, a marked difference in the spectroscopic factors indicates that the full delineation of the transition into the island of inversion remains a challenge for theoretical models.
Neutron-rich nuclei 162,164 Eu were produced by bombarding a proton beam on a 238 U target at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory and mass separating the 162,164 Eu products. New level schemes and new γ-ray transitions of the daughters 162,164 Gd were identified from β-decay spectroscopy studies. Additionally, half-lives of the 162,164 Eu were remeasured to clarify the previous ambiguous results. Two quasiparticle band structures were built and compared with neighboring nuclei. The β and γ bands were extended in 162 Gd and a γ band was extended in 164 Gd. Half-lives of the isomeric states at (6 - ) 1449 keV in 162 Gd and (4 - ) 1096 keV in 164 Gd were measured to be 99(3) μs and 0.56(3) μs, respectively. Projected shell model calculations were performed and found to be in good agreement with all of the experimental data.
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In this work, we present a systematic investigation of few-nucleon systems and light nuclei using the current Low Energy Nuclear Physics International Collaboration interactions comprising semilocal momentum-space regularized two- and three-nucleon forces up to third chiral order (N 2 LO). Following our earlier study utilizing the coordinate-space regularized interactions, the two low-energy constants entering the three-body force are determined from the triton binding energy and the differential cross-section minimum in elastic nucleon-deuteron scattering. Predictions are made for selected observables in elastic nucleon-deuteron scattering and in the deuteron breakup reactions, for properties of the A = 3 and A = 4 nuclei, and for spectra of p-shell nuclei up to A = 16. A comprehensive error analysis is performed including an estimation of correlated truncation uncertainties for nuclear spectra. The obtained predictions are generally found to agree with experimental data within errors. Similarly to the coordinate-space regularized chiral interactions at the same order, a systematic overbinding of heavier nuclei is observed, which sets in for A~10 and increases with A.
Here, the evolution of shell structure around doubly magic exotic nuclei is of great interest in nuclear physics and astrophysics. In the ‘southwest’ region of 78 Ni, the development of deformation might trigger a major shift in our understanding of explosive nucleosynthesis. To this end, new spectroscopic information on key close-lying nuclei is very valuable. We intend to measure the isomeric and β decay of 75 Co, with one-proton and two-neutron holes relative to 78Ni, to access new nuclear structure information in 75 Co and its β-decay daughters 75 Ni and 74 Ni. The nucleus 75 Co is produced in relativistic in-flight fission reactions of 238 U at the Radioactive Ion Beam Factory in the RIKEN Nishina Center. Its isomeric and β decay are studied exploiting the BigRIPS and EURICA setups. We obtain partial β-decay spectra for 75 Ni and 74 Ni, and report a new isomeric transition in 75 Co. The energy [E γ = 1914(2)keV] and half-life [t 1/2 = 13(6) μs] of the delayed γ ray lend support for the existence of a J π = (1/2 – ) isomeric state at 1914(2) keV. A comparison with PFSDG-U shell-model calculations provides a good account for the observed states in 75 Ni, but the first calculated 1/2 – level in 75 Co, a prolate K = 1/2 state, is predicted about 1 MeV below the observed (1/2 – ) level. The spherical-like structure of the lowest-lying excited states in 75 Ni is proved. In the case of 75 Co, the results suggest that the dominance of the spherical configurations over the deformed ones might be stronger than expected below 78 Ni. Further experimental efforts to discern the nature of the J π = (1/2 – ) isomer are necessary.
The observation of secondary γ-rays provides an alternative method of measuring cross sections that populate excited final states in nuclear reactions. The angular distributions of these γ-rays also provide information on the underlying reaction mechanism. Despite a large amount of data of this type in the literature, publicly available R-matrix codes do not have the ability to calculate these types of angular distributions. In this report, the mathematical formalism derived in Brune and deBoer is implemented in the R-matrix code AZURE2 and calculations are compared with previous data from the literature for the 15 N( p, α1γ ) 12 C* reaction. In addition, new measurements, made at the University of Notre Dame Nuclear Science Laboratory using the Hybrid Array of Gamma Ray Detectors (HAGRiD), are reported that span an energy range from E p = 0.88 to 4.0 MeV. Excellent agreement between data and the phenomenological fit is obtained up to the limit of the previous fit at E p = 2.0 MeV and the R-matrix fit is extended from E x ≈ 13.5 up to E x ≈ 15.3 MeV, where 15 N+p and 12 C+α reactions are fit simultaneously for the first time. An excellent reproduction of the 15 N( p, α1γ ) 12 C* and 12 C(α, α) 12 C data is achieved, but inconsistencies and difficulty in fitting other data is encountered and discussed.