Excited Atoms Research Articles

Unveiling the Reaction Mechanism of the N(2D) + Pyridine Reaction: Ring-Contraction versus 7-Membered-Ring Formation Channels.

Despite the relevance of the reactions of the prototypical nitrogen-containing six-membered aromatic molecule (N-heterocyclic) of pyridine (C6H5N) in environmental science, astrochemistry, planetary science, prebiotic chemistry, and materials science, few experimental/theoretical studies exist on the bimolecular reactions involving pyridine and neutral atomic/molecular radicals. We report a combined experimental and theoretical study on the elementary reaction of pyridine with excited nitrogen atoms, N(2D), aimed at providing information about the primary reaction products and their branching fractions (BFs). From previous crossed molecular beam (CMB) experiments with mass-spectrometric detection and present synergistic calculations of the reactive potential energy surface (PES) and product BFs we have unveiled the reaction mechanism. It is found that the reaction proceeds via N(2D) barrierless addition to pyridine that, via bridged intermediates followed by N atom "sliding" into the ring, leads to 7-membered-ring structures. They further evolve, mainly via ring-contraction mechanisms toward 5-membered-ring radical products and, to a smaller extent, via H-displacement mechanisms toward 7-membered-ring isomeric products and their isomers. Using the theoretical statistical estimates, an improved fit of the experimental data previously reported has been obtained, leading to the following results for the dominant product channels: C4H4N (pyrrolyl) + HCN (BF = 0.61 ± 0.20), C3H3N2 (1H-imidazolyl/1H-pyrazolyl) + C2H2 (BF = 0.11 ± 0.06), and C5H4N2 (7-membered-ring molecules or pyrrole carbonitriles) + H (BF = 0.28 ± 0.10). The ring-contraction product channels C4H4N (pyrrolyl) + HCN, C3H3N2 (1H-imidazolyl) + C2H2, C3H3N2 (1H-pyrazolyl) + C2H2, and C5H5 (cyclopentadienyl) + N2 have statistical BFs of 0.54, 0.09, 0.11, and 0.07, respectively. Among the H-displacement channels, the cyclic-CHCHCHCHNCN + H channel and cyclic-CHCHCHCHCN2 + H are theoretically predicted to have a comparable BF (0.07 and 0.06, respectively), while the other isomeric 7-membered-ring molecule + H channel has a BF of 0.03. Pyrrole-carbonitriles and 1H-ethynyl-1H-imidazole (+ H) isomeric channels have an overall BF of 0.03. Implications for the chemistry of Saturn's moon Titan and prebiotic chemistry, as well as for understanding the N-doping of graphene or carbon nanotubes, are noted.

Turbulence Around Auroral Arcs

AbstractThe spectacular visual displays from the aurora come from curtains of excited atoms and molecules, impacted by energetic charged particles. These particles are accelerated from great distances in Earth's magnetotail, causing them to precipitate into the ionosphere. Energetic particle precipitation is associated with currents that generate electric fields, and the end result is a dissipation of the hundreds of gigawatts to terrawatts of energy injected into Earth's atmosphere during geomagnetic storms. While much is known about how the aurora dissipates energy through Joule heating, little is known about how it does so via small‐scale plasma turbulence. Here we show the first set of combined radar and optical images that track the position of this turbulence, relative to particle precipitation, with high spatial precision. During two geomagnetic storms occurring in 2021, we unambiguously show that small‐scale turbulence (several meters) is preferentially created on the edges of auroral forms. We find that turbulence appears both poleward and equatorward of auroral forms, as well as being nestled between auroral forms in the north‐south direction. These measurements make it clear that small scale auroral plasma turbulence is an integral part of the electrical current system created by the aurora, in the sense that turbulent transport around auroral forms enhances ionospheric energy deposition through Joule heating while at the same time reducing the average strength of the electric field.

Dynamics of a two-level atom in the presence of a medium-assisted thermal field

In this paper, the time evolution of a two-level atom in the presence of a medium-assisted thermal field is explored through which the formula for the decay rate of an excited atom is generalized in two aspects. The obtained formula applies to a thermal electromagnetic field as well as to the presence of an arbitrary arrangement of magnetoelectric media. In order to be general with respect to the material environment, the Green’s function approach is used. It is shown that the non-zero temperature contributes to the decay rate via an additive term that is equal to the zero-temperature result multiplied by two times the photon number at the atomic transition frequency.

Electron–ion collision and polarization of X-ray fluorescence radiation under hot quantum plasma conditions

In the current article, the spectral properties and electron collision (total and magnetic) excitation cross sections of ions taking placed in quantum plasmas are investigated. These cross sections are further used to study the polarization and angular distribution characteristics of the de-excitation radiation X-ray spectra, which play an important role in basic theoretical research, the diagnosis of the plasma environment, and the design of optical devices. To do so, a distorted wave method within the relativistic Dirac–Coulomb atomic structure scheme is suggested. The effective interaction potential between electrons and particles in hot quantum plasmas in the method is determined using a quantum approach that incorporates the influence of effective plasma screening effects caused by collective plasma oscillations. This potential replaces the traditional Coulomb interaction potential and is used in solving the modified Dirac equation to obtain the bound and continuum electron wave functions. Higher-order relativistic effects, such as the Breit interaction and the dominant quantum electrodynamics corrections, are added to enhance the accuracy of the method. Detailed calculations for the relativistic atomic structure and collision excitation dynamics process are carried out, taking the highly stripped H-like O7+ ion of astrophysical importance as an illustrative example. Detailed investigations are also conducted on the variation of energies, collision cross sections, and fluorescence polarizations as functions of the plasma parameters. Our results suggest that the joint effects of shielding and plasma coupling lead the energies, cross sections and fluorescence polarizations decrease (compared with the isolated case). The angular distribution of the X-ray fluorescence emission shows large change, suggesting their sensitivity to these effects. This study not only offers a valuable approach to investigating the plasma shielding and plasmon coupling effects in quantum plasmas but also holds significant relevance for applications in controlled nuclear fusion, astrophysical plasmas and so on.

Improvement of mechanical properties by cold plasma treatment of bonded surfaces

In nature, matter is found in solid, liquid or gaseous form. At very high temperatures, molecules can absorb an enormous amount of energy, causing them to move in a disordered way. With the absorbed energy, they can dissociate into atoms, and because of their disordered motion, these molecules or atoms can split into ions and electrons. Excessive heating of matter is therefore always accompanied by ionisation, leaving the medium electrically neutral. This ionised state is known as plasma. It is sometimes called the fourth state of matter. Plasmas are therefore mixtures of neutral and/or excited ions, electrons, atoms, radicals or demodules with an internal energy above the neutral state. Sources of plasma can be as follows: naturally occurring in the ionosphere; produced by nuclear reactions; generated by a hyperfrequency source; formed by direct heating followed by confinement in a region of space by a magnetic field; and produced by electrical discharges. Plasma is characterised by the state of its components: density, which is defined by the number of particles per unit volume; kinetic temperature; and degree of ionisation. Plasma can be thermal or out of thermal equilibrium, or 'cold plasma'. Cold plasma is formed, for example, when a gas passes through strong electric fields - electrons are dissociated from the molecules and the gas becomes electrically conductive and glows blue. The paper describes the equipment used to create cold plasma, which was used to treat different surfaces. After treatment, they were bonded with different adhesives and tested for tensile strenght. An improvement in the mechanical properties mentioned above was observed when the surfaces to be bonded were treated with cold plasma compared to surfaces bonded normally. When the impact of cold plasma treatment on elongation, or ε, is examined, it is found that for Fiber Wood samples, cold plasma treatment considerably boosts elongation, increasing it from 0.35% for untreated samples to 0.81% for samples treated with cold plasma. For samples that have been treated with cold plasma, the average value increases significantly from 0.03% to 0.63% when ArbofillFichte material is used. In addition, the application of cold plasma treatment to the surfaces results in an increase in the modulus of elasticity. For example, the modulus of elasticity doubles for Arbofill Fichte samples, going from 113.56MPa for untreated samples to 227.43MPa for cold plasma treated samples; for Fiber Wood, it increases from an average value of 789.52MPa for untreated samples to an average value of 931.62MPa for treated samples.

Gain measurement of microwave antenna with heterodyne bichromatic excitation in Rydberg atoms.

We propose a scheme for gain measurement of microwave (MW) antenna with heterodyne bichromatic excitation in Rydberg atoms via electromagnetically induced transparency (EIT). The Rydberg-EIT atoms serve as a frequency mixer with a strong locally oscillating MW field and a weak signal field. A large dispersion appears in the EIT windows due to the interference of two sub-EIT systems, which much narrows the transmission spectrum. The locally oscillating MW field could enhance the atomic response to the weak MW signals. The simulation results show that the gain measurement of MW antenna remains good accuracy even for weak MW fields and the minimum detectable MW field strength is about 1/12 of that of common EIT scheme. Other influences on the gain measurement are also investigated.

Observation of Interatomic Coulombic Decay Induced by Double Excitation of Helium in Nanodroplets.

Interatomic Coulombic decay (ICD) plays a crucial role in weakly bound complexes exposed to intense or high-energy radiation. So far, neutral or ionic atoms or molecules have been prepared in singly excited electron or hole states that can transfer energy to neighboring centers and cause ionization and radiation damage. Here we demonstrate that a doubly excited atom, despite its extremely short lifetime, can decay by ICD; evidenced by high-resolution photoelectron spectra of He nanodroplets excited to the 2s2p+ state. We find that ICD proceeds by relaxation into excited He^{*}He^{+} atom-pair states, in agreement with calculations. The ability of inducing ICD by resonant excitation far above the single-ionization threshold opens opportunities for controlling radiation damage to a high degree of element specificity and spectral selectivity.

Steady-state phases and interaction-induced depletion in a driven-dissipative chirally-coupled dissimilar atomic array

A nanophotonic waveguide coupled with an atomic array forms one of the strongly coupled quantum interfaces to showcase many fascinating collective features of quantum dynamics. In particular, for a dissimilar array of two different interparticle spacings with competing photon-mediated dipole-dipole interactions and directionality of couplings, we study the steady-state phases of atomic excitations under a weakly driven condition of laser field. We identify a partial set of steady-state phases of the driven system composed of combinations of steady-state solutions in a homogeneous array. We also reveal the intricate role of the atom at the interface of the dissimilar array in determining the steady-state phases and find an alteration in the dichotomy of the phases strongly associated with steady-state distributions with crystalline orders. We further investigate in detail the interaction-induced depletion in half of the dissimilar array, where the blockaded region results from two contrasting interparticle spacings near the reciprocal coupling regime. This can be further evidenced from the analytical solutions under the reciprocal coupling. Our results can provide insights in the driven-dissipative quantum phases of atomic excitations with nonreciprocal couplings and pave the avenues toward quantum simulations of exotic many-body states essential for quantum information applications. Published by the American Physical Society 2024

Regulatory effect of Tingli Dazao Xiefei Decoction on asthmatic rats by urine metabolomics

Urine metabolomics based on ultra-performance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry(UHPLC-Q-TOF-MS) was utilized to investigate the metabolic regulation mechanism of Tingli Dazao Xiefei Decoction(TLDZ) in rats with allergic asthma. SD male rats were divided into a normal group, a model group, a dexamethasone group, and a TLDZ group. The allergic asthma model was established by intraperitoneal injection of ovalbumin(OVA) to induce allergy, combined with atomization excitation. Urine metabolites from all rats were collected by UHPLC-Q-TOF-MS. The metabolic profiles of rats in each group were built by principal component analysis(PCA). Besides, the differential metabolites between the model group and the TLDZ group were selected by orthogonal partial least squares discriminant analysis(OPLS-DA), t-test(P<0.05), and variable importance in the projection(VIP) values of more than 3. The differential metabolites were identified through HMDB, METLIN, and other online databa-ses. Heat maps and clustering analysis for relative quantitative information of biomarkers in each group were drawn by MeV 4.8.0 software. Finally, MetaboAnalyst, MBRole, and KEGG databases were used to enrich related metabolic pathways and construct metabolic networks. The result demonstrated that TLDZ could effectively regulate the disordered urine metabolic profiles of asthmatic rats. Combined with multivariate statistical analysis and online databases, a total of 45 differential metabolites with significant changes(P<0.05) between the model group and the TLDZ group were screened out. Metabolic pathways including histidine metabolism, tryptophan metabolism, and arginine and proline metabolism were enriched. TLDZ could improve asthma by regulating related metabolic pathways and interfering with pathological processes such as immune homeostasis airway inflammation. The study investigates the molecular mechanism of anti-asthma of TLDZ from the perspective of urine metabolomics, and combined with previous pharmacological studies, it provides a scientific basis for the clinical development and application of TLDZ in the treatment of asthma.

Merits of atomic cascade computations

Atomic cascades refer—first and foremost—to the stepwise de-excitation of excited atoms owing to the emission of electrons or photons. Apart from dedicated experiments at storage rings and synchrotrons, such cascades frequently occur in astro and plasma physics, material research, surface science and at various places elsewhere. In addition, moreover, “atomic cascades” have been found a useful concept for modeling atomic behavior under different conditions, for instance, when dealing with the photoabsorption of matter, the generation of synthesized spectra, or for determining a rather wide class of (plasma) rate coefficients. We here compile and discuss several atomic cascades (schemes) that help predict cross sections, rate coefficients, electron and photon spectra, or ion distributions. We also demonstrate how readily these schemes have been implemented within JAC, the Jena Atomic Calculator. Emphasis is placed on the classification of atomic cascades and their (quite) natural breakdown into cascade computations, to deal with the electronic structure and transition amplitudes of atoms and ions, as well as the cascade simulation of those properties and spectra, that are experimentally accessible. As an example, we show and discuss the computation of dielectronic recombination plasma rate coefficients for beryllium-like gold ions. The concept of atomic cascades and its implementation into JAC can be applied for most ions across the periodic table and will facilitate the modeling and interpretation of many forthcoming observations.Graphical abstract

Delay-induced spontaneous dark-state generation from two distant excited atoms

We investigate the collective non-Markovian dynamics of two fully excited two-level atoms coupled to a one-dimensional waveguide in the presence of delay. We demonstrate that analogous to the well-known superfluorescence phenomena, where an inverted atomic ensemble synchronizes to enhance its emission, there is a “subfluorescence” effect that synchronizes the atoms into an entangled dark state depending on the interatomic separation. The phenomenon can lead to a two-photon bound state in the continuum. Our results are pertinent to long-distance quantum networks, presenting a mechanism for spontaneous entanglement generation between distant quantum emitters. Published by the American Physical Society 2024

New energy levels of atomic holmium discovered by laser spectroscopy in the near infrared spectral range

A combination of optogalvanic spectroscopy and laser-induced fluorescence spectroscopy with a continuous wave tunable single mode Ti-Sa laser was applied to find new energy levels of atomic holmium. Free and excited holmium atoms were produced in a liquid nitrogen-cooled hollow-cathode lamp. In this study, we examined 35 spectral lines of Ho I in the near-infrared wavelength range from 698 nm to 833 nm. Altogether, 16 new energy levels have been discovered, 5 levels of even parity and 11 levels of odd parity. Another four energy levels have been discovered but have already been published by another research group. Data on the hyperfine structure for the new levels are presented. Additionally, hyperfine structure data of three known levels of even parity were determined for the first time. The existence of the new energy levels was confirmed by analyzing 60 lines of previously measured Fourier transform spectra to precisely determine the energy of the levels.

Calculations of Stopping Power, Straggling and Range Projected of FeKr<sup>+</sup>

The present work consists of the simulation of the interaction of a beam of Kr<sup>+</sup> ions with a solid iron target by the software SRIM (Stopping and Range of Ions In Matter). Our goal is to calculate different parameters related to sputtering and ion implantation in a target, such as the spatial distribution of implanted ions, the distributions of electronic and nuclear energy losses as a function of penetration depth and sputtering efficiency, as well as the damage created inside the target. The sputter induced photon spectroscopy technique was used to study the luminescence spectra of the species sputtered from Iron powder, during 5 keV Kr<sup>+</sup> ions bombardment in vacuum better than 107 torr. The optical spectra recorded between 350 and 470 nm exhibit discrete lines which are attributed to neutral excited atoms of Iron (Fe). The experiments are also performed under 105 torr ultra-pure oxygen partial pressure. To ensure the maximum efficiency of molecular modification process, energy of irradiation was decided by using of SRIM software. Based on SRIM simulation of Iron ions interaction with Krypton, the areas on which effect of high energy ions will maximum were predicted. A comparative analysis of molecular before and after irradiation was carried out by scanning electron microscopy. The maximum change in Krypton morphology, in the form of destruction of walls, was appeared at a distance of about μm from the start point of Fe<sup>+</sup> ions track inside the molecular. A substantiation of reason of wall degradation in this area was proposed.

Photochemical surface modification of amorphous carbon thin film to transparency in atmosphere of excited singlet oxygen atoms O(1D) under 157 nm F2 laser irradiation

Amorphous carbon (a-C) thin films have various useful properties; thus, their applications are wide-ranging. These properties are characterized by the ratio of sp3 to sp2 carbon in the thin film, and many studies have been reported on changing this ratio. In this paper, we used an F2 laser with a wavelength of 157 nm to photoexcite the surface of an a-C thin film, and simultaneously photodecompose atmospheric oxygen molecules O2 into excited singlet oxygen atoms O(1D). The results showed that O(1D) atoms can photochemically etch sp2 carbon in thin films significantly better than triplet oxygen atoms O(3P). Thus, we found that the surface layer of the a-C thin film was photochemically modified to be transparent. Raman spectroscopy revealed no change in the chemical bonding state of the transparently modified a-C thin film. On the other hand, in X-ray photoelectron spectroscopy, the intensity of the C 1s peak originated to sp2 carbon decreased. The refractive index was also slightly lowered, probably due to lowering film density. In addition, droplets mainly composed of sp2 carbon generated during thin film deposition were significantly removed after F2 laser irradiation. The electrical resistivity slightly decreased upon F2 laser irradiation and remarkably decreased as the substrate was heated, exhibiting low bandgap properties. Therefore, we succeeded in discovering a new method for changing the ratio of sp3 to sp2 carbon in a-C to be transparent thin film by preferentially generating O(1D) atoms using the F2 laser, as a new elemental technology for fabricating transparent flexible electronic devices.

Optical properties of low-pressure DC Ar plasma torch with N2–SiH4–B2H6 gas mixture injection for Si–B–N thin film deposition

Si–B–N ceramic hard films were prepared by injecting N2+SiH4+B2H6 reaction gas into an argon DC arc plasma jet at reduced pressure. XPS, FT-IR, SEM, and microhardness tester were used to characterize the samples, and the optical properties of Ar discharge plasma jet with and without reaction gas injection were studied by a multichannel high-resolution spectroscopy and a wide spectral range spectroscopy. It is found that the deposited films are mainly composed of Si, B, N and O. The film surface presents a dense structure with hundred-nanometer-sized clusters, and the hardness of sample is greatly enhanced. When the reaction gas is injected into the plasma jet, the emission of excited atoms in the background plasma is greatly reduced, and the growth rate of Si–B–N film shows a significant downward trend as the reaction gas injection ring or substrate holder is moved away from the torch nozzle. A slight enhancement of background plasma emission is observed near the substrate surface with increasing the distance between gas injection ring and torch nozzle, which indicates that the suppression effect of the reactive gas injection on the background plasma emission and the activation efficiency of the reaction gas are weakened, thereby reducing the deposition rate.

On a Spectral Method for β-particle Bound Excitation Collisions in Kilonovae

The interaction of β-particles with the weakly ionized plasma background is an important mechanism for powering the kilonova (KN) transient signal from neutron star mergers. For this purpose, we present an implementation of the approximate fast-particle collision kernel, described by Inokuti following the seminal formulation of Bethe, in a spectral solver of the Vlasov–Maxwell–Boltzmann equation. In particular, we expand the fast-particle plane-wave atomic excitation kernel into coefficients of the Hermite basis, and derive the relevant discrete spectral system. In this fast-particle limit, the approach permits the direct use of atomic data, including optical oscillator strengths, normally applied to photon–matter interaction. The resulting spectral matrix is implemented in the MASS-APP spectral solver framework, in a way that avoids full matrix storage per spatial zone. We numerically verify aspects of the matrix construction, and present a proof-of-principle 3D simulation of a 2D axisymmetric KN ejecta snapshot. Our preliminary numerical results indicate that a reasonable choice of Hermite basis parameters for β-particles in the KN is a bulk velocity parameter u = 0, a thermal velocity parameter α = 0.5c, and a 9 × 9 × 9 mode velocity basis set (Hermite orders of 0–8 in each dimension). For interior-ejecta sample zones, we estimate that the ratio of thermalization from large-angle (≳2.°5) bound excitation scattering to total thermalization is ∼0.002–0.003.

Dipolar focusing in laser-assisted positronium formation

We consider positronium formation in collisions of positrons with excited hydrogen atoms H(n) in an infrared laser field theoretically. This process is assisted by the dipolar focusing effect: a positron moving in a superposition of a laser field and the dipolar field can approach the atomic target even if its trajectory starts with a very large impact parameter, leading to a significant enhancement of the Ps formation cross section. The classical trajectory Monte Carlo method, which is justified for n⩾3 , allows efficient calculation of this enhancement. A similar effect can occur in collisions of positrons with other atoms in excited states, which can lead to improvements in the efficiency of positronium formation.

Dirac-Coulomb-Breit Molecular Mean-Field Exact-Two-Component Relativistic Equation-of-Motion Coupled-Cluster Theory.

We present a relativistic equation-of-motion coupled-cluster with single and double excitation formalism within the exact two-component framework (X2C-EOM-CCSD), where both scalar relativistic effects and spin-orbit coupling are variationally included at the reference level. Three different molecular mean-field treatments of relativistic corrections, including the one-electron, Dirac-Coulomb, and Dirac-Coulomb-Breit Hamiltonian, are considered in this work. Benchmark calculations include atomic excitations and fine-structure splittings arising from spin-orbit coupling. Comparison with experimental values and relativistic time-dependent density functional theory is also carried out. The computation of the oscillator strength using the relativistic X2C-EOM-CCSD approach allows for studies of spin-orbit-driven processes, such as the spontaneous phosphorescence lifetime.

Relativistic calculations of energy levels, lifetimes, transition parameters, and electron impact excitation cross sections for Kr XIX

In this study, we present a detailed analysis of atomic properties for Kr XIX, specifically focusing on the lowest 128 fine-structure levels originating from the 3s23p6, 3s23p53d, 3s3p63d and 3s23p43d2 configurations. We report energy levels, lifetimes, wavelengths, weighted oscillator strengths, and transition probabilities for multipole transition types (E1, E2, M1, and M2). To achieve this, we employed the GRASP2018 code, which implements the fully relativistic multiconfigurational Dirac–Hartree–Fock method and accounts for Breit interaction and quantum electrodynamic effects. We performed another set of calculations using the many-body perturbation theory implemented in the flexible atomic code (FAC). By comparing the results obtained from GRASP2018 and FAC, we established the accuracy and consistency of our calculations. Furthermore, using the relativistic distorted wave theory, we studied electron impact excitation of all transitions to upper levels from the ground and metastable levels and reported excitation cross sections for incident electron energies up to 5 keV. To enhance the practical utility of our findings, we also provided analytical fittings of these cross sections and excitation rate coefficients for their applications in plasma modeling. This work contributes to the atomic properties and excitation cross sections of Kr XIX, addressing a marked gap in the available atomic data.

Adiabatic reactions on excited electronic states of N[formula omitted]O: First computations on the O([formula omitted]P)+N[formula omitted](X)[formula omitted]N([formula omitted]D)+NO(X) and O([formula omitted]P)+N[formula omitted](A)[formula omitted] N([formula omitted]S)+NO(X) reactions

Electronically excited nitrogen atoms and N2 molecules play a major role in nitrogen-rich atmospheres, specially under extreme conditions. Here we computationally explore several excited states of the N2O system and identify two new reactions involving the excited species N2(A) and N(2D) that can occur without electronic transitions. Their rate coefficients are estimated for the first time, and their implication to atmospheric models are discussed. We infer that the O(3P)+N2(A)→N(2D)+NO(X) channel should account for the total experimental NO production at room temperature.