Ground State Resonance Research Articles

Spectroscopy of neutron-unbound27,28F

The ground state of $^{28}$F has been observed as an unbound resonance $2\underline{2}0$ keV above the ground state of $^{27}$F. Comparison of this result with USDA/USDB shell model predictions leads to the conclusion that the $^{28}$F ground state is primarily dominated by $sd$-shell configurations. Here we present a detailed report on the experiment in which the ground state resonance of $^{28}$F was first observed. Additionally, we report the first observation of a neutron-unbound excited state in $^{27}$F at an excitation energy of $25\underline{0}0 (2\underline{2}0)$ keV.

THz Dielectric Properties of Molecular Clusters of PETN and TNT Calculated by Density Functional Theory

The need for better detection of explosive devices has imposed a necessity for determining the dielectric response properties of energetic materials with respect to electromagnetic wave excitation. Among the range of different frequencies for electromagnetic excitation, the THz frequency range is of particular interest because of its nondestructive nature. The present study is based on significant progress in density functional theory (DFT), and associated software technology, which is sufficiently mature for the determination of dielectric response functions, and actually provides complementary information to that obtained from experiment. This point is further demonstrated in this study by calculations of ground state resonance structure associated with molecular clusters of the high explosives PETN and TNT using DFT, which is for the construction of parameterized dielectric response functions for excitation by electromagnetic waves at frequencies within the THz range. These dielectric functions provide for different types of analyses concerning the dielectric response of explosives. In particular, these dielectric response functions provide quantitative initial estimates of spectral response features for subsequent adjustment with respect to additional information such as laboratory measurements and other types of theory-based calculations. With respect to qualitative analysis, these spectra provide for the molecular level interpretation of response structure. The DFT software GAUSSIAN was used for the calculations of ground state resonance structure presented here.

Solvatochromism and Molecular Selectivity of C-(4-chlorophenyl)-N-phenylnitrone: A Photophysical Study

The ground state interaction of C-(4-chlorophenyl)-N-phenylnitrone (N1) with three different α, β-unsaturated ketones (K1 - K3) in very dilute solution (10-6 mol dm-3) has been noticed through charge transfer band formation in the visible region. The experimentally measured transition dipole, ground state resonance energy and formation constants of the complexes indicate interaction selectivity of the acyclic nitrone (N1) for the ketones. Molar absorptivity of the absorbing complexes were determined for all the three N1/K (1:1) interacting systems in toluene. Experimental findings were well rationalized with the help of electron density based global electrophilicity and nucleophilicity indices as well as with frontier molecular orbital calculations.

Dielectric Response of High Explosives at THz Frequencies Calculated Using Density Functional Theory

We present in this study calculations of the ground-state resonance structures associated with the high explosives β-HMX, PETN, RDX, TNT1, and TNT2 using density functional theory (DFT). Our objective is the construction of parameterized dielectric-response functions for excitation by electromagnetic waves at compatible frequencies. These dielectric-response functions provide the basis for analyses pertaining to the dielectric properties of explosives. In particular, these dielectric-response functions provide quantitative initial estimates of spectral-response features for subsequent adjustment with knowledge of additional information, such as laboratory measurements and other types of theory-based calculations. With respect to qualitative analyses, these spectra provide for the molecular-level interpretation of response structure. The DFT software GAUSSIAN was used for the calculations of the ground-state resonance structures presented here.

Temperature and pressure shift of the Cs clock transition in the presence of buffer gases: Ne,N2, Ar

The ground-state hyperfine resonance line of alkali-metal atoms is frequency shifted in the presence of noble or molecular gases. The buffer gases used in vapor-cell atomic clocks thus induce a temperature-dependent shift of the clock transition frequency. We report on measurements of the pressure and temperature dependence of the Cs clock transition frequency in the presence of Ne, Ar, and ${\mathrm{N}}_{2}$ buffer gases. The pressure in the sealed glass vapor cells is measured by means of the shift of the Cs ${D}_{1}$ line. We have also investigated the temperature dependence of the optical shift. From these measurements, we infer the pressure and temperature coefficients of the hyperfine frequency shift. It is then possible to predetermine gas mixture ratios that cancel the temperature sensitivity at a given temperature. This prediction is confirmed experimentally for Ar-N${}_{2}$ mixtures. These results can be useful for improving the long-term frequency stability of Cs vapor-cell clocks.

THz Dielectric Properties of High Explosives Calculated by Density Functional Theory for the Design of Detectors

The current need for better detection of explosive devices has imposed a new necessity for determining the dielectric response properties of energetic materials with respect to electromagnetic wave excitation. Among the range of different frequencies for electromagnetic excitation, the THz frequency range is of particular interest because of its nondestructive nature and ability to penetrate materials that are characteristic of clothing. Typically, the dielectric response properties for electromagnetic wave excitation at THz frequencies, as well as at other frequencies, are determined by means of experimental measurements. The present study, however, emphasizes that density functional theory (DFT), and associated software technology, is sufficiently mature for the determination of dielectric response functions, and actually provides complementary information to that obtained from experiment. In particular, these dielectric response functions provide quantitative initial estimates of spectral response features that can be adjusted with respect to additional information such as laboratory measurements and other types of theory-based calculations, as well as providing for the molecular level interpretation of response structure. This point is demonstrated in the present study by calculations of ground-state resonance structure associated with the high explosives RDX, TNT1, and TNT2 using DFT, which is for the construction of parameterized dielectric response functions for excitation by electromagnetic waves at frequencies within the THz range. The DFT software NRLMOL was used for the calculations of ground-state resonance structure presented here.

Imaginary cubic perturbation: numerical and analytic study

The analytic properties of the ground-state resonance energy E(g) of the cubic potential are investigated as a function of the complex coupling parameter g. We explicitly show that it is possible to analytically continue E(g) by means of a resummed strong coupling expansion, to the second sheet of the Riemann surface, and we observe a merging of resonance and antiresonance eigenvalues at a critical point along the line . In addition, we investigate the convergence of the resummed weak-coupling expansion in the strong-coupling regime, by means of various modifications of order-dependent mappings (ODMs), that take special properties of the cubic potential into account. Various ODMs are adapted to different regimes of the coupling constant. We also determine a large number of terms of the strong-coupling expansion by resumming the weak-coupling expansion using the ODMs, demonstrating the interpolation between the two regimes made possible by this summation method.

Pairing and vibrational correlations in the higher Tamm-Dancoff approximation (HTDA) approach

The higher Tamm-Dancoff Approximation (HTDA) is extended to include vibrational correlations with or without pairing correlations. The residual interaction in use is of the delta (in the $T=1$ channel) plus multipole-multipole type. In this paper we have limited our study to the mere case of isoscalar quadrupole correlations. The approach is illustrated by the consideration of ground state and isoscalar giant quadrupole resonance properties in the $^{40}\mathrm{Ca}$ nucleus.

Anisotropic donor states in electric field

AbstractIn this paper we consider the application of the stabilization method to calculations of the ground state energy and resonance width of shallow donors in a uniform electric field. We show for the first time that within our formulation of this method it is very easy to include various factors influencing electronic structure of shallow impurities, like effective mass anisotropy or magnetic field. We demonstrate that the effective mass anisotropy significantly changes the lifetime of donor bound electrons. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of Debye plasmas on the resonance states of two-electron highly stripped ions using the stabilization method

Effect of Debye plasmas on the bound states and resonance states of two-electron highly stripped ions has been investigated using the stabilization method. Highly correlated exponential basis functions are used to extract resonance parameters. The doubly-excited 1Se resonance energies and widths of two-electron ions having nuclear charge Z are presented as functions of the screening parameters 1/D and 1/Z, with D being the Debye lengths. New results of ground-state energies, resonance energies and widths for the systems with nuclear charge Z = 12 and 14, are reported.

Bound states and resonant states of three self-gravitating Bose-Einstein condensates

The effect of Yukawa potentials on the bound states and resonance states for systems with three self-gravitating bosons and fermions has been investigated using highly correlated basis functions. The complex coordinate rotation method is used to extract resonance parameters. We have investigated the Borromean binding for such systems. The ground and excited state energies, resonance energy and width for the lowest two resonances are reported for different screening parameters along with the critical range for Borromean binding.

Scattering length and effective range for collisions between light ions within a microscopic model

The first coefficients of the effective-range expansion are derived by a direct calculation at zero energy, i.e., without extrapolation, in the generator coordinate version of the resonating-group method. The parameters of the effective nucleon–nucleon interaction are adjusted on available experimental data (phase shifts or binding energies). The scattering length and effective range are determined in this way for the α + n , O 16 + n , C 14 + n neutron scatterings, α + p , O 16 + p , O 14 + p proton scatterings, and α + α , α + H 3 , α + He 3 collisions between light ions. In many cases, neutral and charged, the effective-range expansion is valid up to energies larger than 5 MeV and provide a simple parametrization of the phase shifts. For α + α , the scattering length and effective range can be derived from the properties of the Be 8 ground-state resonance.

Femtosecond Transient Absorption and Nanosecond Time‐Resolved Resonance Raman Study of the Solvent‐Dependent Photo‐Deprotection Reaction of Benzoin Diethyl Phosphate

A combined femtosecond transient absorption (fs-TA) and nanosecond time-resolved resonance Raman (ns-TR3) study was performed to directly detect the dynamics and elucidate the mechanism of the excited state deactivation and solvent-dependent photo-deprotection pathways for benzoin diethyl phosphate (BDP) in neat acetonitrile (MeCN) and 75 % H2O/25 % MeCN. Comparison of the TA spectral evolution observed in the two solvents provides explicit evidence that the photophysical deactivation of the BDP singlet excited state has little solvent dependence. The TA spectra also indicate the related internal conversion (IC) and intersystem crossing (ISC) processes occur rapidly on hundreds of femtoseconds and approximately 2-3 ps time scales, respectively. From this and in conjunction with a photochemistry study and ground state resonance Raman (RR) measurements, the TA results reveal that the phenacyl localized BDP triplet state (that is mainly npi* nature) is the common and immediate precursor to the photo-deprotection reaction in both solvents. However, the triplet deprotection follows different pathways in neat MeCN versus the largely water containing solvent. The deprotection reaction in MeCN was determined to occur with a approximately 11 ns time constant and the reaction was found to be an unimolecular process leading to elimination of the diethyl phosphoric acid apparently concurrent with cyclization to yield the benzofuran product. In the water mixed solvent, the triplet reaction was observed to proceed with a approximately 15 ns time constant and the reaction leads to not only the deprotection-cyclization but also a heterolytic dissociation to release the diethyl phosphate anion through a branching and competing mechanism. The ns-TR3 spectra combined with relevant DFT calculations have been used to characterize the dynamics, structure and vibrational frequencies to help identify the important intermediates as well as to explore the reaction pathway leading to formation of the solvolysis product in the largely water solvent. A consecutive mechanism has been revealed for the heterolysis-solvolysis reaction in the water mixed solvent. The present work provides direct and irrevocable evidence for the dynamics and mechanistic description of the overall photophysics and deprotection related photochemistry for BDP.

“Amide Resonance” Correlates with a Breadth of C−N Rotation Barriers

Complete basis set calculations (CBS-QB3) were used to compute the CN rotation barriers for acetamide and eight related compounds, including acetamide enolate and O-protonated acetamide. Natural resonance theory analysis was employed to quantify the "amide resonance" contribution to ground-state electronic structures. A range of rotation barriers, spanning nearly 50 kcal/mol, correlates well to the ground-state resonance weights without the need to account for transition-state effects. Use of appropriate model compounds is crucial to gain an understanding of the structural and electronic changes taking place during rotation of the CN bond in acetamide. The disparate changes in bond length (DeltarCO << DeltarCN) are found to be consonant with the resonance model. Similarly, charge differences are consistent with donation from the nitrogen lone pair electrons into the carbonyl pi* orbital. Despite recent attacks on the resonance model, these findings demonstrate it to be a sophisticated and highly predictive tool in the chemist's arsenal.

Neutron- 3H potentials and the 5H-properties

The continuum resonance spectrum of 5H ( 3H + n + n ) is investigated by use of the complex scaled hyperspherical adiabatic expansion method. The crucial 3H-neutron potential is obtained by switching off the Coulomb part from successful fits to 3He-proton experimental data. These two-body potentials must be expressed exclusively by operators conserving the nucleon–core mean field angular momentum quantum numbers. The energies E R and widths Γ R of the 1 / 2 + ground-state resonance and the lowest two excited 5 / 2 + - and 3 / 2 + -resonances are found to be ( 1.6 , 1.5 ) MeV, ( 2.8 , 2.5 ) MeV and ( 3.2 , 3.9 ) MeV, respectively. These results agree with most of the experimental data. The energy distributions of the fragments after decay of the resonances are predicted.

Near-Infrared (NIR) to Red and Green Up-Conversion Emission from Silica Sol−Gel Thin Films Made with La0.45Yb0.50Er0.05F3 Nanoparticles, Hetero-Looping-Enhanced Energy Transfer (Hetero-LEET): A New Up-Conversion Process

Bright green and red luminescence has been generated with a 980 nm diode laser from silica sol-gel thin films made with La0.45Yb0.50Er0.05F3 nanoparticles through a newly described hetero-looping-enhanced energy-transfer (hetero-LEET) up-conversion process, which exhibits a power dependence similar to that of a photon avalanche (PA). The hetero-LEET mechanism is potentially more efficient than PA, ground-state absorption/excited-state absorption (GSA/ESA), and energy-transfer (ETU) mechanisms because it combines resonant ground-state absorption with a looping or feedback process.

Ground and Excited State Resonance Raman Spectra of an Azacrown-Substituted [(bpy)Re(CO)3L]+ Complex: Characterization of Excited States, Determination of Structure and Bonding, and Observation of Metal Cation Release from the Azacrown

A [(bpy)Re(CO)3L+] complex (bpy = 2,2'-bipyridine) in which L contains a phenyl-azacrown ether that is attached to Re via an amidopyridyl linking group has been studied by steady state and nanosecond time-resolved resonance Raman spectroscopy. Vibrational band assignments have been aided by studies of model complexes in which a similar electron-donating dimethylamino group replaces the azacrown or in which an electron-donor group is absent, and by density functional theory calculations. The ground state resonance Raman spectra show nu(bpy) and nu(CO) bands of the (bpy)Re(CO)3 group when excitation is exclusively in resonance with the Re --> bpy metal-to-ligand charge-transfer (MLCT) transition, whereas L ligand bands are dominant when it is in resonance with the strong intra-ligand charge-transfer (ILCT) transition present for L ligands with electron-donor groups. Transient resonance Raman (RR) spectra obtained on single color (385 nm) pulsed excitation of the complexes in which an electron-donor group is absent show bpy*- bands of the MLCT excited state, whereas those of the complexes with electron-donor groups show both bpy*- bands and a down-shifted nu(CO) band that together are characteristic of an L-to-bpy ligand-to-ligand charge-transfer (LLCT) excited state. Samples in which a metal cation (Li+, Na+, Ca2+, Ba2+) is bound to the azacrown in the ground state show bands from both excited states, consistent with a mechanism in which the LLCT state forms after metal cation release from the MLCT state. Nanosecond time-resolved RR spectra from two-color (355 nm pump, 500 nm probe) experiments on the electron-donor systems show L-ligand bands characteristic of the LLCT state; the same bands are observed from samples in which a metal cation is bound to the azacrown in the ground state, and their time dependence is consistent with the proposed mechanism in which the rate constant for ion release in the MLCT state depends on the identity of the metal cation.

Quantum mechanical theory of the emission spectrum of Mössbauer sources submitted to self-absorption: An exact result for source line broadening

When a Mössbauer source is prepared using ion implantation, diffusion or any other method, it could be that some resonant ground-state nuclei, as well as the desired resonant-source nuclei, are present in the source. This will lead to source line broadening. Using the coherent-path, quantum mechanical model, for the first time the exact analytical emission line shape from a source containing resonant ground-state nuclei is calculated as a function of the concentration of these resonant ground-state nuclei. For high concentrations the source emission line shape shows the “hole burning” line shape.

Influence of excitons and electric fields on the dielectric function of GaN: Theory and experiment

The shape of the complex dielectric function (DF) of nitride semiconductors in the vicinity of the band gap is strongly influenced by the electron-hole interaction (excitonic effects). Here, the influence of electric fields on the optical response is theoretically studied and compared to experimental data. An exact and numerically fast method is presented allowing the calculation of the imaginary part of the DF in the whole range of reasonable field strengths $F$. The real part of the DF is calculated via the Kramers-Kronig transformation. We discuss how the field influences position, magnitude, and broadening of the ground-state excitonic resonance as well as the absorption far below the band gap. In contrast to the one-electron picture, a linear increase of the energy position of the ground-state resonance is obtained for large $F$ values. Electroreflectance (ER) spectroscopy carried out on an $\mathrm{Al}\mathrm{Ga}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ heterojunction at low temperature demonstrates the sensitivity of the optical response to field changes. Using the calculated field-dependent values of the DF, the ER spectra of both the GaN channel layer and the AlGaN barrier layer are fully reproduced despite the inhomogeneous field distribution. The excellent agreement emphasizes the theoretical approach.

Optical pumping in an RF cooler buncher

The use of optical pumping in an RF linear Paul trap is shown to permit efficient collinear laser spectroscopy in systems where atomic ground state resonance lines are ill-suited to the fast beam technique. The case of yttrium, where laser spectroscopy has been used to study 86–90, 92–102Y and isomeric states of 87–90, 93, 96, 97, 98Y, is highlighted.