Absolute Excitation Research Articles

Probing the structure of X(3872) in photoproduction

We study the production of X(3872) mesons in photon-induced nuclear reactions near the threshold within the collision model based on the nuclear spectral function. The model accounts for direct photon-nucleon X(3872) production processes as well as five different scenarios for their internal structure. We calculate the absolute and relative excitation functions for X(3872) production off 12C and 184W target nuclei at near-threshold incident photon energies of 8–16 GeV, the absolute differential cross sections for their production off these target nuclei at laboratory angles of 0∘–10∘ and for incident photon energy of 13 GeV as well as the A dependences of the relative (transparency ratios) cross sections for X(3872) production from γA collisions at photon energies around 13 GeV within the adopted scenarios for the X(3872) meson internal structure. We show that the absolute and relative observables considered reveal distinct sensitivity to these scenarios. Therefore, the measurement of such observables in a dedicated experiment at the CEBAF facility in the near-threshold energy range will allow us to get valuable information on the X(3872) inner structure.

A study of core-excited states of organic molecules computed with the generalized active space driven similarity renormalization group.

This work examines the accuracy and precision of x-ray absorption spectra computed with a multireference approach that combines generalized active space (GAS) references with the driven similarity renormalization group (DSRG). We employ the x-ray absorption benchmark of organic molecule (XABOOM) set, consisting of 116 transitions from mostly organic molecules [Fransson et al., J. Chem. Theory Comput. 17, 1618 (2021)]. Several approximations to a full-valence active space are examined and benchmarked. Absolute excitation energies and intensities computed with the GAS-DSRG truncated to second-order in perturbation theory are found to systematically underestimate experimental and reference theoretical values. Third-order perturbative corrections significantly improve the accuracy of GAS-DSRG absolute excitation energies, bringing the mean absolute deviation from experimental values down to 0.32eV. The ozone molecule and glyoxylic acid are particularly challenging for second-order perturbation theory and are examined in detail to assess the importance of active space truncation and intruder states.

Single-particle and collective excitations in Zn66

Single-particle and collective excitations in $^{66}\mathrm{Zn}$ have been investigated via the multinucleon transfer reaction, $^{26}\mathrm{Mg}(^{48}\mathrm{Ca}$, $\ensuremath{\alpha}4n\ensuremath{\gamma}$) using the Gammasphere multidetector array and the Fragment Mass Analyzer. In addition to confirming and complementing the previously known low-spin structure, a new quasirotational band comprising several stretched $E2$ transitions has been established to high spins. However, due to fragmentary nature of its decay, it was not possible to link this sequence to the low-lying states and, thus, determine the absolute excitation energies, spins, and parities unambiguously. Large-scale shell-model calculations employing the JUN45 and jj44b effective interactions are able to successfully describe the low-spin structure and herewith confirm that it is dominated by single-particle excitations. The newly established rotational cascade is compared with known superdeformed bands in the $A\ensuremath{\approx}60\text{--}70$ mass region, and with results of calculations performed within the frameworks of the cranked shell model and the adiabatic and configuration-fixed constrained covariant density functional theory and the quantum particle-rotor model.

Regarding the possibility to observe the LHCb hidden-charm strange pentaquark Pcs(4459)0 in antikaon-induced J/ψ meson production on protons and nuclei near the J/ψΛ production threshold

We study the near-threshold J/ψ meson production on protons and nuclei by considering incoherent direct non-resonant K−p→J/ψΛ and two-step resonant K−p→Pcs(4459)0→J/ψΛ charmonium production processes. We calculate the absolute excitation functions, energy and momentum distributions for the non-resonant, resonant and for the combined (non-resonant plus resonant) production of J/ψ mesons off protons as well as off carbon and tungsten target nuclei at near-threshold incident antikaon energies by considering these elementary production channels as well as by assuming the spin-parity assignment of the hidden-charm resonance Pcs(4459)0 with strangeness as JP=(3/2)− within six different scenarios for the branching ratio Br[Pcs(4459)0→J/ψΛ] of the decay Pcs(4459)0→J/ψΛ. We show that the combined observables considered reveal definite sensitivity to these scenarios, which means that they may be an important tool to provide further evidence for the existence of the pentaquark Pcs(4459)0 resonance and to get valuable information on its decay rate to the J/ψΛ final state. Their measurements could be performed in the future at the J-PARC Hadron Experimental Facility.

All-Electron BSE@GW Method for K-Edge Core Electron Excitation Energies.

We present an accurate computational approach to calculate absolute K-edge core electron excitation energies as measured by X-ray absorption spectroscopy. Our approach employs an all-electron Bethe-Salpeter equation (BSE) formalism based on GW quasiparticle energies (BSE@GW) using numeric atom-centered orbitals (NAOs). The BSE@GW method has become an increasingly popular method for the computation of neutral valence excitation energies of molecules. However, it was so far not applied to molecular K-edge excitation energies. We discuss the influence of different numerical approximations on the BSE@GW calculation and employ in our final setup (i) exact numeric algorithms for the frequency integration of the GW self-energy, (ii) G0W0 and BSE starting points with ∼50% of exact exchange, (iii) the Tamm-Dancoff approximation and (iv) relativistic corrections. We study the basis set dependence and convergence with common Gaussian-type orbital and NAO basis sets. We identify the importance of additional spatially confined basis functions as well as of diffuse augmenting basis functions. The accuracy of our BSE@GW method is assessed for a benchmark set of small organic molecules, previously used for benchmarking the equation-of-motion coupled cluster method [Peng et al., J. Chem. Theory Comput., 2015, 11, 4146], as well as the medium-sized dibenzothiophene (DBT) molecule. Our BSE@GW results for absolute excitation energies are in excellent agreement with the experiment, with a mean average error of only 0.63 eV for the benchmark set and with errors <1 eV for the DBT molecule.

Complexation of Green and Red Kaede Fluorescent Protein Chromophores by a Zwitterion to Probe Electrostatic and Induction Field Effects.

The photophysics of green fluorescent protein (GFP) and red Kaede fluorescent protein (rKFP) are defined by the intrinsic properties of the light-absorbing chromophore and its interaction with the protein binding pocket. This work deploys photodissociation action spectroscopy to probe the absorption profiles for a series of synthetic GFP and rKFP chromophores as the bare anions and as complexes with the betaine zwitterion, which is assumed as a model for dipole microsolvation. Electronic structure calculations and energy decomposition analysis using Symmetry-Adapted Perturbation Theory are used to characterize gas-phase structures and complex cohesion forces. The calculations reveal a preponderance for coordination of betaine to the phenoxide deprotonation site predominantly through electrostatic forces. Calculations using the STEOM-DLPNO-CCSD method are able to reproduce absolute and relative vertical excitation energies for the bare anions and anion-betaine complexes. On the other hand, treatment of the betaine molecule with a point-charge model, in which the charges are computed from some common electron density population analysis schemes, show that just electrostatic and point-charge induction interactions are unable to account for the betaine-induced spectral shift. The present methodology could be applied to investigate cluster forces and optical properties in other gas-phase ion-zwitterion complexes.

Experimental modal analysis using velocity feedback excitation

In this study, we proposed a new multi-point excitation method with velocity feedback (FB) excitation to capture the resonance peak clearly as well as a modal identification method. The specific procedure for identifying the modal damping ratio that we proposed is as follows: the modal damping ratio that reduces the damping is designed as the control gain; the reduced modal damping ratio is identified from the frequency response function (FRF) measured by velocity FB excitation using the control gain; and the damping by the control gain is added to identify the original mode damping ratio of the target structure. After summarizing the theory of the proposed methods, we explained their validity by presenting numerical analysis. A two-degree-of-freedom system with high damping characteristics was used, and when absolute and relative velocity FB excitation were applied, the damping of the vibration system was reduced and the FRF was captured. Then, following the procedure of the proposed method, we were able to identify the original modal damping ratio of the target system under consideration. The proposed method is expected to accurately identify the modal characteristics of vibration modes whose resonance peaks do not clearly appear.

Fragment-Based Quantum Mechanical Calculation of Excited-State Properties of Fluorescent RNAs.

Fluorescent RNA aptamers have been successfully applied to track and tag RNA in a biological system. However, it is still challenging to predict the excited-state properties of the RNA aptamer–fluorophore complex with the traditional electronic structure methods due to expensive computational costs. In this study, an accurate and efficient fragmentation quantum mechanical (QM) approach of the electrostatically embedded generalized molecular fractionation with conjugate caps (EE-GMFCC) scheme was applied for calculations of excited-state properties of the RNA aptamer–fluorophore complex. In this method, the excited-state properties were first calculated with one-body fragment quantum mechanics/molecular mechanics (QM/MM) calculation (the excited-state properties of the fluorophore) and then corrected with a series of two-body fragment QM calculations for accounting for the QM effects from the RNA on the excited-state properties of the fluorophore. The performance of the EE-GMFCC on prediction of the absolute excitation energies, the corresponding transition electric dipole moment (TEDM), and atomic forces at both the TD-HF and TD-DFT levels was tested using the Mango-II RNA aptamer system as a model system. The results demonstrate that the calculated excited-state properties by EE-GMFCC are in excellent agreement with the traditional full-system time-dependent ab initio calculations. Moreover, the EE-GMFCC method is capable of providing an accurate prediction of the relative conformational excited-state energies for different configurations of the Mango-II RNA aptamer system extracted from the molecular dynamics (MD) simulations. The fragmentation method further provides a straightforward approach to decompose the excitation energy contribution per ribonucleotide around the fluorophore and then reveals the influence of the local chemical environment on the fluorophore. The applications of EE-GMFCC in calculations of excitation energies for other RNA aptamer–fluorophore complexes demonstrate that the EE-GMFCC method is a general approach for accurate and efficient calculations of excited-state properties of fluorescent RNAs.

Structure of high-lying levels populated in the 96Y →96Zr β decay

The nature of the high-lying final levels of the 96Ygsβ decay, one of the three most important contributors to the high-energy reactor antineutrino spectrum, has been investigated in high-resolution γ-ray spectroscopy following the β decay as well as in a campaign of inelastic photon scattering experiments. The comprehensive approach establishes 1− levels associated with the Pygmy Dipole Resonance as high-lying final levels in the β decay. Branching ratios extracted from β decay complement photon scattering and allow the absolute E1 excitation strength to be determined for levels populated in both reactions. The combined data represents a comprehensive approach to the wavefunction of the 1− levels below the Qβ value, which are investigated in the Quasiparticle Phonon Model. The calculations reveal that the components populated in β decay contribute only with small amplitudes to the complex wavefunction of these 1− levels. A comparison of the β decay results to data from total absorption γ-ray spectroscopy demonstrates a good agreement between both measurements.

Assessment of local coupled cluster methods for excited states of BODIPY/Aza‐BODIPY families

It was previously reported that Laplace transformed local CC2 (LCC2*) provided the best agreement (MAE = 0.145 eV) when comparing vertical excitation energies to experimental λmax for a benchmark set of 17 BODIPY/Aza-BODIPY molecules. However, these energies did not agree with values obtained from canonical CC2. Here we report LCC2* computations of vertical excitation energies on the same benchmark set of molecules using a newly implemented treatment of the ground state. Comparison with resolution-of-identity approximate coupled cluster to second-order (RI-CC2) results demonstrate that the new LCC2* results agree quantitatively. Furthermore, these values can easily be corrected empirically to also provide excellent agreement with the experiment. We show that the local algebraic diagrammatic construction to second-order (LADC(2)) method exhibits the same differences between implementations as seen for LCC2. The source of the difference is traced to an improved treatment of the ground state in the local methods, which decreases agreement with the experiment (as attributed to a fortuitous cancellation of errors) but significantly improves agreement with RI-CC2. While the absolute vertical excitation energies now show larger deviations, there remains a strong linear correlation between the LCC2* results and the experiment. For the 17 BODIPY/Aza-BODIPY molecules vertical excitation energies are determined using DLPNO-STEOM-CCSD and shown to have excellent agreement with experimental λmax (MAE = 0.145 eV), which is the best of all the single-reference methods. The vertical excitation energies are determined using LCC2*, empirically corrected LCC2*, and RI-CC2 for a series of eight large BODIPYs and Aza-BODIPYs.

Photoemission resulting from collisions of I2 with 5–100 eV electrons

We have determined absolute apparent excitation cross sections for photoemission in the 300–1050 nm spectral region resulting from collisions of I2 with electrons of 4.8–100 eV translational energy. Experiments were done in single collision conditions and emission is observed from I2, I2 +, I and I+. All the emission features appear to turn on at the energy thresholds for formation of the respective excited state species. At higher electron beam energy the spectra are dominated by emissions from the strong I2 + A–X band, as well as the intense emission from several I 5s 25p 46s states. An attempt to determine the initial I2 + A populations generated from electron impact is discussed. These populations are determined from simulations of the I2 + A–X emission band using both experimentally and theoretically determined potential energy surfaces available in the literature. Direct, vertical formation of I2 + A from I2 X is only supported in the case of the ab initio potential energy surface.

Possibility of observation of hidden-bottom pentaquark resonances in bottomonium photoproduction on protons and nuclei near threshold

We study the meson photoproduction on protons and nuclei at near-threshold center-of-mass energies below 11.4 GeV (or at the corresponding photon laboratory energies below 68.8 GeV). We calculate the absolute excitation functions for the nonresonant and resonant photoproduction of mesons off protons at incident photon laboratory energies of 63-68 GeV by considering direct ( ) and two-step ( , , ) production channels within different scenarios for the nonresonant total cross section of the elementary reaction and for branching ratios of the decays , , and . We also calculate an analogous function for the photoproduction of mesons on the 12C and 208Pb target nuclei in the near-threshold center-of-mass beam energy region of 9.0-11.4 GeV by considering the respective incoherent direct ( ) and two-step ( , , and , , ) ) production processes using a nuclear spectral function approach. We demonstrate that a detailed scan of the total photoproduction cross section on proton and nuclear targets in the near-threshold energy region in future high-precision experiments at the proposed high-luminosity electron-ion colliders EIC and EicC in the US and China should provide a definite result for or against the existence of the nonstrange hidden-bottom pentaquark states and ( =1, 2, 3) as well as clarify their decay rates.

The possibility to study in-medium modification of J/ψ mesons from their photoproduction on nuclei near threshold in the case of presence of the LHCb pentaquark states [formula omitted], [formula omitted] and [formula omitted] in this photoproduction

We study the J/ψ photoproduction from nuclei in the near-threshold beam energy region of Eγ=5–11 GeV within the nuclear spectral function approach by considering incoherent direct (γN→J/ψN) and two-step (γp→Pc+(4312), Pc+(4312)→J/ψp; γp→Pc+(4440), Pc+(4440)→J/ψp; γp→Pc+(4457), Pc+(4457)→J/ψp) J/ψ production processes. We calculate the absolute excitation functions for the non-resonant and resonant production of J/ψ mesons off 12C and 208Pb target nuclei within the different scenarios for in-medium modification of the directly photoproduced J/ψ mesons and for branching ratios of the decays Pc+(4312)→J/ψp, Pc+(4440)→J/ψp and Pc+(4457)→J/ψp. We show that the non-resonant subthreshold J/ψ production in γA reactions reveals some sensitivity to employed in-medium modification scenarios for J/ψ mesons, which is not masked by the resonantly produced J/ψ mesons, only if above branching ratios are less than 5%. We also demonstrate that if these branching ratios more than 5% then the presence of the Pc+(4312), Pc+(4440) and Pc+(4457) resonances in J/ψ photoproduction on nuclei produces above threshold additional enhancements in the behavior of the total J/ψ creation cross section on nuclei, which could be also studied in the future JLab experiments at the CEBAF facility to provide both further evidence for their existence and valuable information on their nature.

Low energy (6-18 eV) electron scattering from condensed thymidine (dT) III: absolute electronic excitation cross sections.

Absolute cross sections (CSs) for electronic excitation by low-energy electron (LEE) scattering, from condensed thymidine (dT) in the 6-18 eV incident energy range, were measured by high-resolution electron energy loss spectroscopy (HREELS). Various electron energy loss (EEL) spectra were acquired using 1 ML of dT condensed on a multilayer film of Ar held at about 20 K under ultra-high vacuum (∼1 × 10-11 Torr). dT is one of the most complex DNA constituents to be studied by HREELS and these spectra provide the first LEE energy-loss data for electronic excitation of a nucleoside. CSs for transitions to the states 13A', 13A'', 23A', 21A', 33A', 23A'', 43A', 33A'', 53A' and 51A' of dT were extracted from the EEL spectra. These states correlate to those previously measured for the thymine moiety. Two broad resonances are observed in the energy dependence of the CSs at around 8 and 10 eV; these energies are close to those found in earlier gas- and solid-phase studies on the interaction of LEEs with dT, thymine and related molecules. A quantitative comparison between the electronic CSs of dT and those of thymine and tetrahydrofuran indicates that no variation is induced in the electronic CSs of thymine upon chemically binding to a deoxyribose group.

Towards a determination of absolute cross sections for projectile excitation of hydrogen‐like uranium in collisions with neutral atoms

Recently, the contribution of the generalized Breit interaction to electron impact ionization was identified for the first time in a high‐Z system, namely, hydrogen‐like uranium. This study employed a measurement of the relative population of the j = 1/2 and j = 3/2 states of the L shell by projectile excitation in collision of U91+ with hydrogen and nitrogen targets. However, for a rigorous test of ion–atom collision theory, also the absolute excitation cross sections are of great importance. In the present work, we report on our efforts to extend the previous study to a determination of the absolute projectile excitation cross sections by normalization to the well‐known radiative electron capture process.

New and Efficient Equation-of-Motion Coupled-Cluster Framework for Core-Excited and Core-Ionized States.

We present a fully analytical implementation of the core-valence separation (CVS) scheme for the equation-of-motion (EOM) coupled-cluster singles and doubles (CCSD) method for calculations of core-level states. Inspired by the CVS idea as originally formulated by Cederbaum, Domcke, and Schirmer, pure valence excitations are excluded from the EOM target space and the frozen-core approximation is imposed on the reference-state amplitudes and multipliers. This yields an efficient, robust, practical, and numerically balanced EOM-CCSD framework for calculations of excitation and ionization energies as well as state and transition properties (e.g., spectral intensities, natural transition, and Dyson orbitals) from both the ground and excited states. The errors in absolute excitation/ionization energies relative to the experimental reference data are on the order of 0.2-3.0 eV, depending on the K-edge considered and on the basis set used, and the shifts are systematic for each edge. Compared to a previously proposed CVS scheme where CVS was applied as a posteriori projection only during the solution of the EOM eigenvalue equations, the new scheme is computationally cheaper. It also achieves better cancellation of errors, yielding similar spectral profiles but with absolute core excitation and ionization energies that are systematically closer to the corresponding experimental data. Among the presented results are calculations of transient-state X-ray absorption spectra, relevant for interpretation of UV-pump/X-ray probe experiments.

An apparatus and methodology for high-power SQUID-detected ferromagnetic resonance measurements

Historically, ferromagnetic resonance has been dominated by inductive techniques, for the best part of the last 80 years. It has been only in the last 20 years that non-inductive techniques, such as Ferromagnetic Resonance Force Microscopy (FMRFM) and Magneto-optical Kerr Effect (MOKE), have been used to study, for example, the spatial distribution of resonance modes. Neither of these techniques is absolute - i.e. provides information on the amplitude of excitation as a function of absorbed microwave power. Here we extend on the recent demonstration of SQUID-detected FMR [J. M. O’Reilly and P. Stamenov, Rev. Sci. Instrum. 89, 044701 (2018)], of absolute scalar resonance measurements in single-crystalline and poly-crystalline YIG, at various fields and temperatures, by introducing a new set-up, where the microwave power, instead of being sunk in a matched load at the cryogenic end of the measurement probe is brought back to the ambient environment and is both metered and sunk in high dissipation power (&amp;gt;50 W @ 50 Ω) matching load. The here suggested methodology allows for the absolute excitation amplitude of modes excited during high-power operation of critical microwave devices, such as filters and Y-junction stripline circulators, to be predicted based on direct measurements of the same material in a known geometry.

Convex Optimization for Array Diagnosis Using Amplitude-Only Far Field Data in Impulsive Noise Environment

In this paper, an array diagnosis method using amplitude-only far-field data in impulsive noise environment is proposed. For amplitude-only far-field data, the power of the observed field is quadratic with respect to array excitation, which leads to a nonlinear inverse problem to restore array excitation. Such a nonlinear inverse problem is transformed into a linear inverse problem, where array excitation vector is replaced by a lifted vector. Based on the structure of the lifted vector, an absolute array excitation vector that has an identical structure to that of array excitation vector is defined. Since these two vectors share the same structure, it is assumed that they also share the same kind of probability distribution. Specifically, the generalized Gaussian distribution with different parameters to address different element failing rates is used to model the probability distribution of the real array excitation vector and the absolute array excitation vector. To model the impulsive noise, the Laplacian probability distribution function is used. The maximum a posterior criterion is adopted to formulate the optimization problem that is eventually found to be convex. However, this convex optimization problem does not have an analytical solution. To solve it, a proximal gradient method is applied, which yields an iterative update algorithm. Finally, computer simulations and experiment are conducted to verify the validity and superiority of the proposed method.

Low energy (1-19 eV) electron scattering from condensed thymidine (dT) I: absolute vibrational excitation cross sections.

Absolute cross sections (CSs) for vibrational excitation by electrons of energy between 1-19 eV scattering from condensed thymidine (dT) were measured by means of high-resolution electron energy loss spectroscopy (HREELS). The CSs were extracted from electron energy loss spectra of dT condensed on multilayers film of Ar held at about 20 K under ultra-high vacuum (∼1 × 10-11 Torr). dT is one of the most complex molecules to be studied in condensed phase by HREELS. The magnitudes of the vibrational CSs lie within the 10-17 cm2 range. Structures observed in the energy dependence of the vibrational CSs under 3 eV and around 4 eV were compared with previous results of gas- and solid-phase studies on dT and related molecules (e.g., thymine and tetrahydrofuran). These structures were attributed to the formation of shape resonances.

Note: Absolute electronic excitation cross sections for 8.5-17.5 eV electron scattering from condensed dimethyl phosphate (DMP).

Note: Absolute electronic excitation cross sections for 8.5-17.5 eV electron scattering from condensed dimethyl phosphate (DMP).