Isomeric State Research Articles

Laser spectroscopy of triply charged 229Th isomer for a nuclear clock.

Thorium-229 (229Th) possesses an optical nuclear transition between the ground state (229gTh) and low-lying isomer (229mTh). A nuclear clock based on this nuclear-transition frequency is expected to surpass existing atomic clocks owing to its insusceptibility to surrounding fields1-5. In contrast to other charge states, triply charged 229Th (229Th3+) is the most suitable for highly accurate nuclear clocks because it has closed electronic transitions that enable laser cooling, laser-induced fluorescence detection and state preparation of ions1,6-8. Although laser spectroscopic studies of 229Th3+ in the nuclear ground state have been performed8, properties of 229mTh3+, including its nuclear decay lifetime that is essential to specify the intrinsic linewidth of the nuclear-clock transition, remain unknown. Here we report the trapping of 229mTh3+ continuously supplied by a 233U source and the determination of nuclear decay half-life of the isolated 229mTh3+ to be through nuclear-state-selective laser spectroscopy. Furthermore, by determining the hyperfine constants of 229mTh3+, we reduced the uncertainty of the sensitivity of the 229Th nuclear clock to variations in the fine-structure constant by a factor of four. These results offer key parameters for the 229Th3+ nuclear clock and its applications in the search for new physics.

Optically Distinguishable Electronic Spin-isomers of a Stable Organic Diradical.

Herein, we introduce a model of electronic spin isomers, the electronic counterpart of nuclear spin isomers, by using a stable organic diradical. The diradical, composed of two benzotriazinyl radicals connected by a rigid triptycene skeleton, exhibits a small singlet-triplet energy gap of -3.0 kJ/mol, indicating ca. 1:1 coexistence of the two spin states at room temperature. The diradical shows characteristic near-IR absorption bands, which are absent in the corresponding monoradical subunit. Variable temperature measurements revealed that the absorbance of the NIR band depends on the abundance of the singlet state, allowing us to identify the NIR band as the singlet-specific absorption band. It enables photoexcitation of one of the two spin states coexisting in thermal equilibrium. Transient absorption spectroscopy disclosed that the two spin states independently follow qualitatively different excited-state dynamics. These results demonstrate a novel approach to the design and study of electronic spin isomers based on organic diradicals.

Photophore-Anchored Molecular Switch for High-Performance Nonvolatile Organic Memory Transistor.

Over the past decade, molecular-switch-embedded memory devices, particularly field-effect transistors (FETs), have gained significant interest. Molecular switches are integrated to regulate the resistance or current levels in FETs. Despite substantial efforts, realizing large memory window with a long retention time, a critical factor in memory device functionality, remains a challenge. This is due to the inability of an isomeric state of a molecular switch to serve as a stable deep trap state within the semiconductor layer. Herein, the study addresses this limitation by introducing chemical bonding between molecular switch and conjugated polymeric semiconductor, facilitating closed isomer of diarylethene (DAE) to operate as a morphologically stable deep trap state. Azide- and diazirine-anchored DAEs are synthesized, which form chemical bonds to the polymer through photocrosslinking, thereby implementing permanent and controllable trapping states nearby conjugated backbone of polymer semiconductor. Consequently, when diazirine-anchored DAE is blended with F8T2 and subjected to photocrosslinking, the resulting organic FETs exhibit remarkable memory performance, including a memory window of 22 V with a retention time over 106 s, a high photoprogrammable on/off ratio over 103, and a high operational stability over 100 photocycles. Further, photophore-anchored DAEs can achieve precise patterning, which enables meticulous control over the semiconductor layer structure.

Comment on "Nuclear Excitation by Free Muon Capture".

Comment on "Nuclear Excitation by Free Muon Capture".

Prompt neutron emission in 250No spontaneous fission associated with ground and isomeric state decays

Abstract The complete-fusion reaction 204Pb(48Ca,2n)250No was used to study two activities of 250No with distinct half-lives. A total of 1357 events were observed in the SFiNx neutron detection system. The average number of neutrons emitted per spontaneous fission of 250No was determined to be . The unusually symmetrical shape of the prompt neutron multiplicity distribution was restored and presented for the first time. Statistical tests were performed to compare the prompt neutron multiplicity distributions associated with the ground state and K-isomer state decays.

Theoretical study of the photoisomerization of 1,2-bispyrazinyl-ethylene and the halogen ion salts of 1-Pyrazinyl-2-(4’-methylpyrazinyl)ethylene

ContextIt has been reported that photoexcitation of azastilbene compounds like E-1,2-bispyrazinyl-ethylene (bpe) can undergo E → Z photoisomerization of its quaternary salts via the excited triplet state. However, experimentally it is possible to get low fluorescence and photoisomerisation quantum yields in a state with higher internal conversion than intersystem crossing. We modelled bpe and its methylated derivative (bpeMe), as well as its quaternary halogen salts (bpeMeX with X = F−, Cl−, Br− and I−) to study levels of fluorescence, phosphorescence and excited state potential energy surfaces (PES). Results support experimental observations of molecules where the anion of a salt is an efficient electron donor, that molecules with weak electron-donating anions like Cl− to give increased fluorescence and photoisomerization, as compared to molecules with stronger electron-donating anions like I−, which are dominated by competing electron transfer. The fluorescence of bpeMeF and bpeMeCl was found to be stronger than bpeMeBr and bpeMeI. A deep well in the triplet excited state of bpeMeI is considered responsible for the decreased photoisomerization, compared to what was experimentally observed for bpeMeCl. Uniquely, the bpeMeI molecule is characterised by near-zero splitting of the s1 and t1 excited states that can enhance charge transfer. The quaternary salt of bpeMe with stronger electron-donating Br− anion was observed to undergo fluorescence and phosphorescence at much lower energy compared to those with weak electron-donating F− and Cl− anions. This research shows how to control the excited state fluorescence, phosphorescence and isomerization of quaternary halogen salts of methyl derivatives of 1,2-bispyrazinyl-ethylene, which aids experimental design where excited state isomerization is considered.MethodsGeometry optimization, molecular electrostatic potential (MESP), and time dependent density functional theory (TDDFT) calculations were conducted utilizing Gaussian 16 with the B3LYP functional and the 6–31 + G(d,p) basis set. The minimum energy path (MEP) for the E to Z isomerization of the molecules was established employing the Nudged-Elastic-Band (NEB) method, implemented in Orca 4.2. Precise energies of the E → Z isomerization reaction path were determined employing CASSCF and a more accurate multireference method, NEVPT2.

High-K isomers in a self-consistent mean-field approach with the Gogny force

High-K isomeric states in even–even nuclei are described within a mean-field framework with full blocking and using the finite range Gogny force. Theoretical calculations of low energy spectra of several nuclei across the nuclear chart are compared with equal filling approximation results and experimental data. Despite the global character of the employed interactions, a good agreement between the different many-body methods and experimental data is found.

Stability of a photosurfactant-laden viscous liquid thread under illumination

This paper investigates the effects of a light-actuated photosurfactant on the canonical problem of the linear stability of a viscous thread surrounded by a dynamically passive fluid. A model consisting of the Navier–Stokes equations and a set of molar concentration equations is presented that capture light-induced switching between two stable surfactant isomer states, trans and cis. These two states display significantly different interfacial properties, allowing for some external control of the stability behaviour of the thread via incident light. Normal modes are used to generate a generalized eigenvalue problem for the growth rate which is solved with a hybrid analytical and numerical method. The results are validated with appropriate analytical solutions of increasing complexity, beginning with a solution to a clean interface, then analytical solutions for one insoluble surfactant, one soluble surfactant and a special case of two photosurfactants with a spatially uniform undisturbed state. Presenting each of these cases allows for a holistic discussion of the effect of surfactants in general on the stability of a liquid thread. Finally, the numerical solutions in the presence of two photosurfactants that display radially non-uniform undisturbed states are presented, and details of the impact of the illumination on the linear stability of the thread are discussed.

Nuclear isomers in medicine

Only a small handful of nuclear isomers plays an important role in modern medicine. However, one single isomer (Tc-99m) is in terms of quantitative use almost the foundation of the medical application of radioactive compounds. This single isomer has driven the development of modern nuclear medicine over half a century. It is used for diagnostic imaging every day and all over the world. The nuclear and atomic physics basis for this is explained. The main areas of nuclear medicine (diagnostic single photon imaging, diagnostic positron emitter imaging and therapeutic use) are explained, and the few important isomers used in each category are exposed. Although nuclear medicine is evolving rapidly and making important gains in the management of oncological, cardiological and neurological diseases, new radionuclides and new isomers are rarely introduced. The medical use is confined to a narrow set of radionuclides close to the line of stability, and here, of course, the nuclear properties in general and the characteristics of the isomeric states are well known, and possible medical usage has been considered repeatedly. The nuclear isomers will probably keep their role, but from basic physics point of view, just as useful but trivial example of applied nuclear physics.

Comprehensive Analysis of Coupled Proline Cis-Trans States in Bradykinin Using ωBP-REMD Simulations.

It is well-known that proline (Pro) cis-trans isomerization plays a decisive role in the folding and stabilization of proteins. The conformational coupling between isomerization states of different Pro residues in proteins during conformational adaptation processes is not well understood. In the present work, we investigate the coupled cis-trans isomerization of three Pro residues using bradykinin (BK), a partially unstructured nonapeptide hormone, as a model system. We use a recently developed enhanced-sampling molecular dynamics method (ω-bias potential replica exchange molecular dynamics; ωBP-REMD) that allows us to exhaustively sample all combinations of Pro isomer states and obtain converged probability densities of all eight state combinations within 885 ns ωBP-REMD simulations. In agreement with experiment, the all-trans state is seen to be the preferred isomer of zwitterionic aqueous BK. In about a third of its structures, this state presents the characteristic C-terminal β-turn conformation; however, other isomer combinations also contribute significantly to the structural ensemble. Unbiased probabilities can be projected onto the peptide bond dihedral angles of the three Pro residues. This unveils the interdependence of the individual Pro isomerization states, i.e., a possible coupling of the different Pro isomers. The cis/trans equilibrium of a Pro residue can change by up to 2.5 kcal·mol-1, depending on the isomerization state of other Pro residues. For example, for Pro7, the simulations indicate that its cis state becomes favored compared to its trans state when Pro2 is switched from the trans state to the cis state. Our findings demonstrate the efficiency of the ωBP-REMD methodology and suggest that the coupling of Pro isomerization states may play an even more decisive role in larger folded proteins subject to more conformational restraints.

Nuclear isomers at the extremes of their properties

Nuclear isomers at the extremes of their properties

Nuclear photonics and nuclear isomers

Nuclear photonics and nuclear isomers

Multi-neutron-hole and core-excited configurations of isomeric states near the doubly-magic $$^{208}$$Pb

Multi-neutron-hole and core-excited configurations of isomeric states near the doubly-magic $$^{208}$$Pb

The LSU-Argonne conversion electron spectrometer: A new detector for the X-Array and SATURN decay station

A new conversion electron detector has been commissioned at the ATLAS/ CARIBU facility at Argonne National Laboratory. The LSU-Argonne Conversion Electron Spectrometer (LACES) is a LN2-cooled Si(Li) detector system designed to be incorporated into a decay station that comprises the dedicated HPGe clover array with a box geometry (X-Array) and the Scintillator and Tape Using Radioactive Nuclei (SATURN) device. This integration enables simultaneous measurements of conversion electrons and gamma-rays in decay experiments, yielding novel information on transition multipolarities, electric monopole transitions, and isomeric states that decay mostly via conversion electrons. A measurement of the energy resolution of LACES yielded 2.3-keV FWHM at 975 keV for electrons and 1.3-keV FWHM at 75 keV for X-rays. A detailed study of the absolute detection efficiency (at 5 mm from the source) was performed, where this quantity was determined experimentally in the range of electron transition energies between 25.5 keV and 1047.8 keV and subsequently simulated using the GEANT4 code. Measurement and simulations are found to be in excellent agreement. A precise characterization, for this type of detector system, of the absolute detection efficiency for such a wide energy range is reported for the first time.

Hyperpolarized long-lived spin state of methylene protons of 2-bromoethanol obtained from ethylene with non-equilibrium nuclear spin order

In this work we achieve a significant overpopulation (PLLS≈1%) of the long-lived spin state (LLS) of methylene protons in 2-bromoethan(2H)ol (BrEtOD) obtained in a reaction between ethylene with non-equilibrium nuclear spin order and bromine water. Given all protons in ethylene are magnetically equivalent, its nuclear states are classified into nuclear spin isomers (NSIM) with total spin I = 2,1,0. Addition of parahydrogen to acetylene produces ethylene with a population of only those NSIMs with I = 1,0. As a result of the reaction with bromine water the non-equilibrium spin order of ethylene is partly transferred to the singlet LLS involving the two methylene groups of BrEtOD. The 1H NMR signal enhancement (SE≈200) obtained as a result of the LLS readout is approximately equal to the SE of the hyperpolarized BrEtOD obtained with a single π/4 pulse. The LLS relaxation time (TLLS) was shown to be approximately 40 s (≈8T1) in the argon-bubbled sample.

Geometry-induced Oligomerization of Fluorine-substituted Phenylazothiazole Photoswitches.

Photoswitches are molecules that can absorb light of specific wavelengths and undergo a reversible transformation between their trans and cis isomeric forms. In phenylazo photoswitches, it is common for the less stable cis (Z) isomer to convert back to the more stable trans (E) isomer either through photochemical or thermal means. In this research, we designed new derivatives of phenylazothiazole (PAT) photoswitches, PAT-Fn, which feature fluorine substituents on their phenyl component. These derivatives can reversibly isomerize under visible light exposure with the enrichment of E and Z isomers at photostationary state (PSS). Surprisingly, we observed an unconventional phenomenon when these PAT-Fn (n ≧2) photoswitches were in their cis isomeric state in the absence of light. Instead of the anticipated transformation from cis to trans isomer, these compounds converted to an oligomeric compound. Our detailed experimental investigation and theoretical calculations, indicated the crucial role of fluorine substituents and the distinctive geometric arrangement of the cis isomer in driving the unexpected oligomerization process originating from the cis isomeric state.

Systematic shell-model study for structure and isomeric states in 200−210Po isotopes

We report systematic large-scale shell-model calculation for Po isotopes with A= 200 to 210. We have performed calculations using KHH7B interaction in the model space Z = 58-114 and N = 100-164 around doubly-magic 208Pb. We allow valence neutrons to occupy in the 1f5/2, 2p3/2, 2p1/2, and 0i13/2 orbitals, while two valence protons beyond Z=82 are occupied in 0h9/2, 1f7/2 and 0i13/2 orbitals. The calculated energies and electromagnetic properties are compared with the available experimental data and predicted where experimental data are not available. We have also reported shell-model results for different isomeric states of these nuclei.

Exploring the low-lying electronic states of C4H6OS isomers, dihydro-2(3H)-thiophenone and dihydro-3(2H)-thiophenone

Results of a detailed study on the electronic state spectroscopy of C4H6OS isomers, dihydro-2(3H)-thiophenone and dihydro-3(2H)-thiophenone, have been obtained from high-resolution vacuum ultraviolet photoabsorption experiments together with quantum chemical calculations. The absolute photoabsorption cross-sections in the 3.7–10.7 eV energy range were obtained at the AU-UV beam line, ASTRID2 synchrotron radiation facility. The absorption spectra exhibit features due to transitions into valence and Rydberg states, superimposed on vibrational fine structure which appear much weaker in the photoabsorption spectrum of dihydro-3(2H)-thiophenone. Assignments have been proposed for some of the absorption bands with the aid of ab initio calculations at the equation-of-motion coupled-cluster singles and doubles level (EOM-CCSD) providing vertical excitation energies and oscillator strengths. The nature of the transitions was assessed by visual inspection of the natural orbitals for each transition and the average values from the electronic radial spatial extents of the electronic cloud. A comparison between the vibrational structure observed in the experimental spectra suggests relevant CO stretching excitations for both molecules, with important CH2 twisting and rocking modes for dihydro-2(3H)-thiophenone and ring stretching modes for dihydro-3(2H)-thiophenone. Photolysis lifetimes from 0 up to 50 km altitude in the Earth's atmosphere for both chemical compounds have been estimated from the absolute photoabsorption cross-sections.

Mass spectrometry approaches to natural and synthetic melanin characterization

AbstractCharacterization of synthetic and natural melanin nanoparticles (MNPs) has been challenging due to the variability of properties and chemical bonding. Although eumelanin was the first to be discovered, four additional subcategories of melanin now exist including pheomelanin, neuromelanin, allomelanin and pyomelanin. Mass spectrometry (MS) methods have provided crucial insights into the bonding, structure, and mechanism regarding MNP formation, but inconsistent findings in the literature have caused further confusion in the analysis and structure of MNPs. This mini‐review will focus on the types of MS experiments that have been used to analyze MNPs and what kind of information can be gained from different ionization sources, collisional activation experiments, and reaction monitoring quantitative methods when analyzing different subcategories of MNPs. Additionally, future directions regarding alternative applications of MNPs in MS experiments, mass defect analyses of complex mixtures, and a standardized nomenclature for isomeric redox states will all be addressed. © 2023 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.

Isomerization dynamics of a novel cis/trans‐only merocyanine

AbstractMerocyanines (MC) usually adopt ring opened zwitterionic structures that are interconvertible with their ring‐closed spiropyran photoisomers. By methylating the phenolate oxygen, and thereby blocking the ring‐closure reaction, a cis/trans‐only MC photoswitch was obtained, yielding a perfect candidate for a detailed examination of the cis/trans isomerization mechanism for this class of compounds. This photoswitch displays outstanding properties including excellent photoreaction quantum yields and photoswitching turnovers. Due to the central polymethine bridge of MC, in principle eight cis (C)/trans/(T) isomers are possible. Density Functional Theory (DFT) calculations revealed the CCT and TTT‐isomers of the studied compound as most stable cis and trans ground state isomers, respectively. UV/vis transient absorption studies combined with conical intersection computations with the complete active space self‐consistent field (CASSCF) method show that both trans/cis‐ and cis/trans‐photoisomerizations are initiated by a rotation of the central doubled bond fragment. A hot ground state species is then formed, which undergoes a second isomerization. Thus, the cis/trans reaction proceeds via a CCT‐CTT‐TTT sequence and the reverse reaction via TTT‐TCT‐CCT.