1s State Research Articles

Oscillatory Photoelectron Signal of N-Methylmorpholine as a Test Case for the Algebraic-Diagrammatic Construction Method of Second Order.

Motivated by recent progress in the application of time-resolved photoelectron spectroscopy (TRPES) to molecular Rydberg states, we report herein a detailed assessment of the performance of the second-order algebraic diagrammatic construction (ADC(2)) method in the simulation of their TRPES spectra. As the test case, we employ the tertiary aliphatic amine N-methylmorpholine (NMM), which is notable for the fact that the signal of its 3s state exhibits long-lived oscillations along the electron binding energy axis. The relaxation process of photoexcited NMM is simulated via the Born-Oppenheimer molecular dynamics method, and the resulting TRPES spectrum is generated on the basis of ionization energies and approximate Dyson orbital norms calculated with the continuum orbital technique. On the whole, the simulated TRPES spectrum achieves satisfactory agreement with experiment, which suggests that the ADC(2) method provides a realistic description of the potential energy surfaces of the relevant excited and ionized states. In particular, the simulations reproduce the fine oscillatory structure of the signal of the 3s state, and provide evidence to the effect that it results from a coherent vibrational wavepacket evolving along the deformation modes of the six-membered ring. However, it is found that ADC(2) underestimates electron binding energies by up to a few tenths of an electronvolt. The case of NMM demonstrates the usefulness of ADC(2) as a tool to aid the interpretation of the TRPES spectra of large organic molecules.

Recent Advances Concerning the 87Sr Optical Lattice Clock at the National Time Service Center

We review recent experimental progress concerning the 87Sr optical lattice clock at the National Time Service Center in China. Hertz-level spectroscopy of the 87Sr clock transition for the optical lattice clock was performed, and closed-loop operation of the optical lattice clock was realized. A fractional frequency instability of 2.8 × 10−17 was attained for an averaging time of 2000 s. The Allan deviation is found to be 1.6 × 10−15/τ1/2 and is limited mainly by white-frequency-noise. The Landé g-factors of the (5s2)1S0 and (5s5p)3P0 states in 87Sr were measured experimentally; they are important for evaluating the clock’s Zeeman shifts. We also present recent work on the miniaturization of the strontium optical lattice clock for space applications.

Study of \u03d2 production in pPb collisions at sqrt{s_{mathrm{NN}}}=8.16 TeV

The production of ϒ(nS) mesons (n = 1, 2, 3) in pPb and Pbp collisions at a centre-of-mass energy per nucleon pair sqrt{s_{mathrm{NN}}}=8.16 TeV is measured by the LHCb experiment, using a data sample corresponding to an integrated luminosity of 31.8 nb−1. The ϒ(nS) mesons are reconstructed through their decays into two opposite-sign muons. The measurements comprise the differential production cross-sections of the ϒ(1S) and ϒ(2S) states, their forward-to-backward ratios and nuclear modification factors. The measurements are performed as a function of the transverse momentum pT and rapidity in the nucleon-nucleon centre-of-mass frame y* of the ϒ(nS) states, in the kinematic range pT < 25 GeV/c and 1.5 < y* < 4.0 (−5.0 < y* < −2.5) for pPb (Pbp) collisions. In addition, production cross-sections for ϒ(3S) are measured integrated over phase space and the production ratios between all three ϒ(nS) states are determined. Suppression for bottomonium in proton-lead collisions is observed, which is particularly visible in the ratios. The results are compared to theoretical models.

A charged particle veto detector for kaonic deuterium measurements at DAΦNE

The antikaon-nucleon interaction close to threshold provides crucial information on the interplay between spontaneous and explicit chiral symmetry breaking in low-energy QCD. In this context, the importance of kaonic deuterium x-ray spectroscopy has been well recognized, but no experimental results have yet been obtained due to the difficulty of the measurement. To measure the shift and width of the kaonic deuterium 1s state with an accuracy of 30 eV and 75 eV, respectively, an apparatus is under construction at the Laboratori Nazionali di Frascati. A detailed Monte Carlo simulation has shown that an increase of the signal to background ratio by a factor of ten will be required compared to the successfully performed kaonic hydrogen measurement (SIDDHARTA). Three pillars are essential for the newly developed experimental apparatus: a large area x-ray detector system (consisting of Silicon Drift Detectors), a lightweight cryogenic target system and a veto system, consisting of an outer veto detector (Veto-1) for active shielding and an inner veto detector (Veto-2) for charged particle suppression. For both veto systems, an excellent time resolution is required to distinguish kaons stopping in gas from direct kaon stops in the entrance window or side wall of the target. First test measurements on the Veto-2 system were performed. An average time resolution of (54 ± 2) ps and detection efficiencies of ~ 99 % were achieved.

FAMU: study of the energy dependent transfer rate Λμp → μO

The main goal of the FAMU experiment is the measurement of the hyperfine splitting (hfs) in the 1S state of muonic hydrogen ΔEhfs (μ-p)1S. The physical process behind this experiment is the following: μp are formed in a mixture of hydrogen and a higher-Z gas. When absorbing a photon at resonance-energy ΔEhfs ≈ 0.182 eV, in subsequent collisions with the surrounding H2 molecules, the μp is quickly de-excited and accelerated by ∼ 2/3 of the excitation energy. The observable is the time distribution of the K-lines X-rays emitted from the μZ formed by muon transfer (μp) + Z → (μZ)* + p, a reaction whose rate depends on the μp kinetic energy. The maximal response, to the tuned laser wavelength, of the time distribution of X-ray from K-lines of the (μZ)* cascade indicate the resonance. During the preparatory phase of the FAMU experiment, several measurements have been performed both to validate the methodology and to prepare the best configuration of target and detectors for the spectroscopic measurement. We present here the crucial study of the energy dependence of the transfer rate from muonic hydrogen to oxygen (Λμp → μ0), precisely measured for the first time.

Wavelength-Dependent Nonlinear Optical Absorption and Broadband Optical Limiting in Au-Fe2O3-rGO Nanocomposites

Broadband optical limiting and wavelength-dependent nonlinear absorption studies of Au-Fe2O3-(15, 25, 40 wt %)rGO (reduced graphene oxide) nanocomposites were investigated using the Z-scan technique and excited with femtosecond (700–900 nm, 80 MHz, 150 fs) laser pulses. A reduction in the graphene perfect (La) domain and ID/IG ratio observed in the Raman data and the appearance of a Au 4f and Fe 2p singlet along with a shift in the C 1s state toward higher energy in the XPS data, peak broadening in the XRD data, and different mass residues left out with respect to content of rGO in the TG-DTA data strongly indicated the incorporation of Au-Fe2O3 nanostructures on solar exfoliated reduced graphene oxide. Selected aread electron diffraction data ascertained the presence of Au and Fe2O3 as a composite, and transmission electron microscopy (TEM) data revealed that the nano-octahedra Au-Fe2O3 turned themselves into nanospindles during incorporation of rGO. Ground state absorption spectra illustrated a pure and...

Phase-resolved optical emission spectroscopy of a transient plasma created by a low-pressure dielectric barrier discharge jet

A transient plasma created by a low-pressure dielectric-barrier discharge operated with argon was investigated by means of optical emission spectroscopy and imaging. Images of the discharge and emission spectra were recorded with sub-phase resolution and relative densities of excited argon states were obtained. Profiles of densities and electron temperatures were evaluated for the discharge cycle by comparison with results of a collisional-radiative model (CRM). To overcome difficulties in sub-cycle modelling of the important argon 1s states, a combination of the CRM with a density estimation based on radiation-trapping is proposed. Absolute densities of all four 1s states were measured and additionally verified by tunable laser absorption spectroscopy. The presented combination may help to improve optical diagnostics of rare gas plasmas in cases were the dominating processes for the 1s states are not known with sufficient accuracy.

Is bottomonium suppression in proton-nucleus and nucleus-nucleus collisions at LHC energies due to the same effects?

We show that we can reproduce all the features of the bottomonium suppression in both proton-nucleus and nucleus-nucleus collisions at LHC energies in a comover-interaction picture. For each collision system, we use the measured relative suppression of the excited ϒ(2S) and ϒ(3S) states to ϒ(1S) by ATLAS and CMS to parametrise the scattering cross sections of all S- and P -wave bottomonia with the comoving particles created during the collisions. In addition to a single nonperturbative parameter, these cross sections depend on the momentum distribution of these comovers which we found to be the same for proton-nucleus and nucleus-nucleus collisions as well as for partonic and hadronic comovers. Moreover, we can also reproduce the absolute suppresion rates measured by ALICE, ATLAS, CMS and LHCb when the nuclear modifications of the parton densities are taken into account.

Practical approach for beryllium atomic clusters: TD-DFT potential energy surfaces from equilibrium to dissociation for excited states of 2s → 2p

To shed light on the spectroscopic energy-smearing mechanism of the recently developed technique for multi-element analysis (e.g., forensic tests on artworks), which is called plume laser-induced fluorescence, practically computer simulations need to be accurate and fast enough for generating wide-range excited-state potential energy surfaces (PESs) from equilibrium to dissociation of large (non-equilibrated) atomic clusters. Currently, all the very high-level post-Hartree–Fock theories (e.g., coupled-cluster theory) are computationally too expensive for this purpose (e.g., taking at least ~ 23 years). After considering the extensive applications of time-dependent density-functional theory (TD-DFT) in computing the optical properties of many-body systems, we wonder how TD-DFT performs in the wide-range-PES generations because no such TD-DFT application is found by us in the literature (perhaps due to its insufficient static/non-dynamical correlation energy). In this work, we carried out TD-DFT calculations on beryllium atomic clusters from Be1 to Be50 (in contrast to open-shell H2 or Li2 system, we think the individual closed-shell Be systems at the dissociation limit could help TD-DFT to describe the static/non-dynamical correlation. For example, it is usually considered that Be2 has zero non-dynamical correlation energy in the literature) with and without Tamm–Dancoff approximation (TDA). Electronic excited-state properties (e.g., PES, equilibrium position, dissociation energy, fork intersection) associated with 2s → 2p are systematically investigated at a total of 48 levels of TD-DFT. Our calculations are thoroughly benchmarked against experimental results and (very) high-level theoretical values. In short, we find that for accurate simulations, it is necessary to use diffuse basis sets and the TDA approximation. TD-DFT with the small basis set 3-21+G* took ~ 2 min to finish a single-point excitation energy calculation on a linear Be50 (a toy model), while the large basis set 6-311+G(2df,2p) took 30 min. By contrast, a couple-cluster theory EOM-CCSD with 6-311+G(2df,2p) took 2.5 h to do the same but merely for a smaller linear Be10. In general, we suggest that TD-DFT:TDA with 3-21+G* should be practically fast and accurate enough for emulating our desired wide-range excited-state PESs of large Be atomic clusters (including conical intersection points of close energies) in the future studies. Nevertheless, benchmarking work on (much) larger sizes of Be clusters will always be more desirable whenever its computational costs at very high level of theories becomes more tractable.

Magnetic orbit-orbit interaction involving electrons and the nucleus orbiting around the center of mass in 1S and 1P Rydberg states of helium. Finite-nuclear-mass calculations with explicitly correlated Gaussian functions.

An finite-nuclear-mass (FNM) approach is employed to describe the magnetic orbit-orbit interaction of the electrons and the nucleus orbiting around the center of mass of the helium atom in 1S and 1P Rydberg states. The calculations are performed using explicitly correlated Gaussian functions to expand the states’ wave functions. The non-linear parameters of the Gaussians are optimized using a variational approach employing the analytical energy gradient. An FNM and INM (infinite-nuclear-mass) approaches are used in the optimization and compared.

Trajectory surface hopping study of the photodissociation dynamics of methyl radical from the [formula omitted] and [formula omitted] Rydberg states

The photodissociation dynamics of methyl radical from selected vibrational levels of the 3s and 3pz Rydberg states has been studied using the trajectory surface hopping method on one-dimensional potential energy curves along the carbon-hydrogen dissociative coordinate and the non-adiabatic couplings between them, calculated by ab initio methods. Lifetimes and product distributions have been obtained for all the studied vibrational levels and compared with previous theoretical and experimental works. The theoretical lifetimes tend to decrease as vibrational excitation increases in accordance with experimental results. The agreement, however, is only qualitative considering the reduced dimensionality of the model.

Transient processes under excitation of ultrashort laser pulses in colloidal solutions of CdSe/ZnS quantum dots.

We present that in the case of picosecond durations, the limitation efficiency of laser radiation and absorption kinetics in CdSe/ZnS colloidal solutions is determined by Auger relaxation through the 1S(e) states. In the observed kinetics of a probe-pulse transmission, the "delayed limitation" effect has been detected. Numerical modeling has made it possible to identify the competition between the next two relaxation processes of highly excited states: relaxation through size quantization levels and phononless relaxation through traps states.

Ground state of ultrashallow thermal donors in silicon

We have found ultrashallow thermal donors (USTDs) in carbon- and hydrogen-doped Czochralski silicon (CZ-Si) crystals, in which the electronic structure obeys the effective-mass theory. To the best of our knowledge, these are the shallowest energy levels among those of the currently reported donors in Si crystals. In addition, the ground state (1s state) of USTDs was found to be split into at least two. In this study, we measured the temperature dependence of the transmittance induced by the transition from the ground state or upper ground state to the 2p+− and 2p0 states of USTD-1 and USTD-3. It was found that the energy levels of the upper ground state of USTD-3 are shallower than those of USTD-1 despite the fact that the ground state of USTD-1 is shallower than that of USTD-3. That is, the energy levels of the upper ground state of USTD-1 and USTD-3 are inverted against those of the ground state. In addition, we compared the electron spin resonance of 13C (nuclear spin I = 1/2)- and deuterium (I = 1)-doped Si with that of 12C (I = 0)- and hydrogen (I = 1/2)-doped Si. However, no clear difference was found between the electron spin resonance spectra of the two. On the basis of these results, we briefly discuss the atomic structure of the USTDs.

Detection of atomic oxygen O(3PJ) with vacuum ultraviolet emission subsequent to two-photon absorption

Observation of infrared emission following two-photon absorption has been widely employed to detect atomic oxygen O(3PJ) so far. In the present study, a method of detecting O(3PJ) with vacuum ultraviolet (VUV) instead of infrared emission has been developed. The scheme of detection is (i) 2p33p3PJ ←← 2p43PJ (UV two-photon absorption); (ii) 2p33p3PJ → 2p33s3S (transfer to the 3S state); and (iii) 2p33s3S → 2p43PJ (VUV emission). The present method is favorable under the conditions at high ambient pressures because the effect of undesirable collisional quenching is smaller than that on the detection of infrared. An application to the kinetic measurement relevant to O(3PJ) also has been demonstrated.

First-principles DFT calculations of the electronic structure and optical properties of TlInGe2Se6, a prospective NLO material

We present results of first-principles density functional theory (DFT) calculations of total density of states (DOS) and partial densities of states (PDOSs) of novel quaternary selenide TlInGe2Se6, a promising nonlinear optical (NLO) material. The calculations are performed employing the augmented plane wave + local orbitals (APW + lo) method as implemented in the WIEN2k package. The DOS and PDOSs curves reveal the significant hybridization between the electronic states of atoms composing the TlInGe2Se6 compound and forming its chemical bonds. The present DFT calculations indicate that the Se 4p states are the principal contributors to the valence band of TlInGe2Se6, making the main contributions to the top and upper portion of the band, while contributions of the Ge 4p and In 5s states dominate in its central portion and bottom, respectively. Furthermore, contributions of the unoccupied Ge 4s states dominate at the bottom of the conduction band of the compound under study. The calculated electronic bands along broad selected symmetry paths manifest that the conduction band minimum and the valence band maximum are positioned at the L point of the first Brillouin zone resulting in a direct band gap of the compound under consideration. The main optical constants, namely dispersion of the absorption coefficient, real and imaginary parts of dielectric function, electron energy-loss spectrum, refractive index, extinction coefficient and optical reflectivity are studied for TlInGe2Se6 based on the APW + lo calculations.

Proton scattering from excited states of atomic hydrogen

Wavepacket continuum-discretisation approach is used to calculate excitation, ionization and electron-capture (ec) cross sections for proton collisions with n = 2 states of atomic hydrogen, where n is the principal quantum number. The approach assumes a classical motion for the projectile and is based on the solution of the three-body Schrödinger equation using the two-center expansion of the total scattering wave function. The scattering wave function is expanded in an orthonormal basis set built from negative-energy eigenstates and wavepacket pseudostates representing the continuum of both the target atom and the atom formed by the projectile after capturing the electron. With a sufficiently large basis, due to the strong coupling between channels, the method produces converged cross sections for direct-scattering, ionization and ec processes simultaneously. For the quasi-elastic transitions, where both orbital and magnetic quantum numbers change, the integrated cross section is infinite. Nevertheless, the corresponding transitions probabilities are finite at any given impact parameter, indicating that the angular differential cross sections can be measured. Calculated cross sections for scattering on the metastable 2s state are compared with other theoretical results obtained using atomic-orbital close-coupling and classical-trajectory Monte Carlo approaches. Considerable disagreement with previous calculations has been found for some transitions at various incident energies.

A Method for Measuring the Weak Value of Spin for Metastable Atoms.

A method for measuring the weak value of spin for atoms is proposed using a variant of the original Stern–Gerlach apparatus. A full simulation of an experiment for observing the real part of the weak value using the impulsive approximation has been carried out. Our predictions show a displacement of the beam of helium atoms in the metastable state, , that is within the resolution of conventional microchannel plate detectors indicating that this type of experiment is feasible. Our analysis also determines the experimental parameters that will give an accurate determination of the weak value of spin. Preliminary experimental results are shown for helium, neon and argon in the and metastable states, respectively.

Electronic and magnetic properties of Al-doped WS2 monolayer under strain

Magnetic properties of Al-doped WS2 monolayer under strain are investigated by ab initio methods. Without strain, the Al-doped WS2 monolayer is a nonmagnetic nano material. We applied strain to Al-doped WS2 monolayer from –10% to 10%. Under tensile strain, ranging from 3% to 10%, the system always keeps nonmagnetic and changes from semiconductor to metal-like material. The magnetic moment gets a maximum value of 3.03 μB at –3% compressive strain. However, the magnetic moment of system decreases to zero gradually as the compressive strain increases. The coupling among the 3s states of Al, 5d states of W and 3p states of S is responsible for the strong strain effect on the magnetic properties. Our studies predict Al-doped WS2 monolayer under strain to be candidates for application in spintronics.

Electronic band-structure and optical constants of Pb2GeS4: Ab initio calculations and X-ray spectroscopy experiments

The electronic band-structure of the ternary sulfide Pb2GeS4 was investigated by combining experimental and theoretical methods. Binding energy (BE) values of core electrons of Pb2GeS4 are measured employing X-ray photoelectron spectroscopy (XPS) for as-synthesized and treated with Ar+-ions crystal surfaces. The XPS measurements indicate that Ar+-ion treatment does not change the BE values of the core-level electrons of atoms constituting the Pb2GeS4 single crystal as well as peculiarities of the XPS valence band (VB) spectrum. The treatment does not cause changes in the crystal surface stoichiometry. The band-structure calculations based on density functional theory (DFT) reveal total density of states and partial densities of states of Pb2GeS4 within different exchange–correlation approximations. The best fit with the experiment is derived when the DFT calculations of Pb2GeS4 employ modified Becke-Johnson potential with Hubbard-corrected functional and taking into account spin–orbit (SO) interaction. The calculations indicate that top and upper portion of the VB is composed mainly by S 3p states, its central portion is formed by Ge 4p and S 3p states, while contributions of Pb 6s states dominate at its bottom with slightly smaller contributions of Ge 4s states as well. Contributions of unoccupied Pb 6p states dominate at the conduction band (CB) bottom. Regarding the occupation of the VB by Ge 4p and S 3p states, the theoretical data are confirmed experimentally by matching the XPS VB spectrum on a common energy scale with the X-ray emission spectra representing the valence S p and Ge p states. The present calculations yield that the VB maximum is positioned at the Y point, while the CB minimum at the Г point; this fact indicates that Pb2GeS4 sulfide is an indirect-gap material. The principal optical constants are also elucidated using the ab initio DFT calculations.

TlInGe2S6, A Prospective Nonlinear Optical Material: First-Principles DFT Calculations of the Electronic Structure and Optical Properties

We report on results of first-principles density functional theory (DFT) calculations of the total density of states (DOS) and the partial densities of states of a quaternary TlInGe2S6 compound, a promising nonlinear optical material. The calculations are made using the augmented plane wave + local orbitals method employing the WIEN2k package. The DOS curves are calculated in different approaches for exchange-correlation potentials, and it has been established that the best coincidence with the experiment is achieved when modified Becke–Johnson exchange potential is used with correction parameter U and an account of the spin–orbit splitting effect. The present DFT calculations present that the S 3p states are the primary contributors to the TlInGe2S6 valence band, making the main input to its top and upper portion. The primary contributors to the central portion of the valence band of TlInGe2S6 are the Tl 6s and Ge 4p states, while its bottom is generated due to contributions of mainly the In 5s states with slightly smaller contributions of the Ge 4p states as well. The bottom of the conduction band is dominated by the unoccupied Ge 4s states. The conduction band minimum and the valence band maximum are located at the L point of the first Brillouin zone resulting in a direct band gap of the TlInGe2S6 compound. The key optical constants are elucidated for TlInGe2S6 based on the present DFT calculations.