Values Of Excitation Energy Research Articles

First-principles extrapolation method for accurate CO adsorption energies on metal surfaces

We show that a simple first-principles correction based on the difference between the singlet-triplet CO excitation energy values obtained by density-functional theory (DFT) and high-level quantum chemistry methods yields accurate CO adsorption properties on a variety of metal surfaces. We demonstrate a linear relationship between the CO adsorption energy and the CO singlet-triplet splitting, similar to the linear dependence of CO adsorption energy on the energy of the CO $2\ensuremath{\pi}*$ orbital found recently [Kresse et al., Phys. Rev. B 68, 073401 (2003)]. Converged DFT calculations underestimate the CO singlet-triplet excitation energy $\ensuremath{\Delta}{E}_{\mathrm{S}\ensuremath{-}\mathrm{T}},$ whereas coupled-cluster and configuration-interaction (CI) calculations reproduce the experimental $\ensuremath{\Delta}{E}_{\mathrm{S}\ensuremath{-}\mathrm{T}}.$ The dependence of ${E}_{\mathrm{chem}}$ on $\ensuremath{\Delta}{E}_{\mathrm{S}\ensuremath{-}\mathrm{T}}$ is used to extrapolate ${E}_{\mathrm{chem}}$ for the top, bridge, and hollow sites for the (100) and (111) surfaces of Pt, Rh, Pd, and Cu to the values that correspond to the coupled cluster and CI $\ensuremath{\Delta}{E}_{\mathrm{S}\ensuremath{-}\mathrm{T}}$ value. The correction reproduces experimental adsorption site preference for all cases and obtains ${E}_{\mathrm{chem}}$ in excellent agreement with experimental results.

Stopping powers of polycarbonate for 0.36–5.94-MeV protons and 1.0–24.0-MeV α particles

The stopping powers of polycarbonate for protons of energy 0.6–5.9 MeV and α particles of energy 2.0–24.0 MeV have been measured in a transmission experiment employing thin-foil targets. The essence of the novel experimental method employed in the present measurements is to record both projectile energy and time of flight while constantly alternating measurements with and without the target foil in place. The accuracies of the proton data and α-particle data range from 2.0% to 3.0% and 2.2% to 2.7%, respectively. All of the resulting measurements were analyzed in terms of modified Bethe–Bloch theory in order to extract values of the target mean excitation energy (I) and Barkas-effect parameter (b). The composite results for the two projectiles are that I=71.52 eV and b=1.13, the former value lying about one standard deviation below the additivity value and the latter value lying about one standard deviation below the expected value of 1.4±0.1. Previous measurements of the stopping power of polycarbonate for Li7 ions were analyzed by the same method, but with the inclusion of an effective charge parameter (λ). The proton and α-particle data, with a few lower-energy points included, were analyzed for a three-parameter fit, also. Results for the three projectiles studied indicate both internal consistency and agreement with expectations based on modified Bethe–Bloch theory.

Energies and Dipole Moments of Excited States of Ozone and Ozone Radical Cation Using Fock Space Multireference Coupled-Cluster Analytical Response Approach

Using the Fock space multireference coupled-cluster (FS-MRCC) analytical linear response approach, we report the dipole moments of low-lying singlet and triplet excited states of ozone. The low-lying singlet and triplet excited states are calculated at the ground-state geometry and at the adiabatic geometry for the 1A2 and 1B1. For comparison we also calculate at the ground-state geometry the dipole moments of the 1A2, 1B1 and 1B2 using multireference configuration interaction (MRCI) with a bigger VQZ basis and complete active space. We also report as by-product the excitation energy values in the singles and doubles approximation. At the ground-state geometry we also report the energy and the dipole moments of the 2A1, 2A2 and 2B1 states of the ozone radical cation. The energy of the ozone cation radical is compared with the other correlated approaches. It matches well with the experimental values.

Theoretical investigation on the N+SF2→NS+ reaction involving resonance-enhanced multiphoton ionization process

NS + was detected from ionization of the final product of the N(2D)+SF2 reaction by laser multiphoton ionization. NS is not the spectral carrier of our REMPI (resonance-enhanced multiphoton ionization) spectrum. For understanding the experimental facts and to obtain a complete description of the whole process, quantum-chemical calculations were performed. The density functional theory/Becke’s three-parameter hybrid-function calculations indicate that NSF is the product of the most favorable channel of the N+SF2 reaction. The complete active space self-consistent field (CASSCF) potential energy curve calculations predict that 1 1A″ is a predissociative state of NSF with the NS radical and F atom as the dissociation products. The CASSCF vibrational frequencies calculated at the 1 1A″ minimum are in line with the excitation spectrum. The CASPT2 adiabatic excitation energy value of 3.32 eV for the 1 1A″ state is close to the energy value (3.44 eV) of one photon. On the basis of theoretical calculations, it is concluded that NS+ detected in the experiments is produced by one-photon dissociation and ionization of the 1 1A″ excited state of NSF, which is the product of the most favorable channel of the N+SF2 reaction.

Particle spectroscopy of low-lying collective states in 100Ru

One neutron stripping and pick-up results obtained in São Paulo with good energy resolution show that levels interpreted in previous works as two-phonon and three-phonon states in 100Ru are excited with considerable intensity through predominantly direct one-step single neutron transfers. Furthermore, a comparative analysis of excitation energy values obtained in recent experiments, including the present results, with previous ones shows that there are at least 4 spurious levels in the adopted 100Ru level scheme below 2.5 MeV. Several levels seen in recent gamma work are here confirmed and three new ones indicated below 3.2 MeV of excitation energy.

Analysis of measurements of stopping powers of formvar, polyimide, polysulfone, and vyns for 3.6 to 10.5 MeV 7Li ions

AbstractThe stopping powers of formvar, polysulfone, polyimide, and vyns for 7Li projectiles have been measured with the transmission technique and thin foil targets. The experimental data have been analyzed in terms of modified Bethe–Bloch theory to extract characteristic values of the mean excitation energy and Barkas effect parameter, as well as to study the effects of including a single effective charge parameter. Results of this investigation are in general supportive of the outcomes of earlier similar studies with protons and α‐particles traversing the same target materials in the sense that previously reported trends in projectile‐dependent behavior of values of mean excitation energy and Barkas effect parameter are followed in most cases. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002

Intermediate Hamiltonian Fock-space coupled cluster method in the one-hole one-particle sector: Excitation energies of xenon and radon

The intermediate Hamiltonian Fock-space coupled cluster method developed recently is applied to excitations in the one-hole one-particle sector, taking xenon and radon atoms as test cases. Virtual orbitals are modified to yield better approximations to orbitals occupied in excited states. The usual Fock-space coupled cluster scheme diverges for these systems, but the intermediate Hamiltonian approach converges for large P spaces and yields excitation energies in very good agreement with experiment. The average error in the calculated values for the lowest excitation energies (about 20 for each atom) is 0.6%. Predictions are made for the unobserved 8s Rydberg states of Rn.

Analyses of stopping power measurements for 0.90–2.50 MeV protons and deuterons traversing Al 2O 3 targets

Recently reported measurements of the stopping power of Al 2O 3 for 0.90–2.50 MeV protons and deuterons have been analyzed in terms of modified Bethe–Bloch theory. Values of the mean excitation energy ( I) and Barkas-effect parameter ( b) have been extracted from the data, yielding results for I and b, respectively, of 176.8 eV and 0.83 for protons, and of 182.7 eV and 1.02 for deuterons. These values of I exceed the additivity-based value by 32% for proton data and by 36% for deuteron data. Moreover, both extracted values of b lie well below the expected interval of 1.3–1.5.

High-spin states of 8838Sr50: breaking of the neutron core

The nucleus 88Sr has been produced at high spin as fission fragment following the fusion reaction 28Si + 176Yb at 145 MeV bombarding energy. The γ-rays were detected with the Eurogam2 array. The level scheme of 88Sr has been extended up to 8.5 MeV excitation energy and spin values around 14ℏ. The structure of the high-energy states is discussed by analogy with those of the even–even neighbouring N=50 isotones and possible configurations are proposed. They are compared with results obtained within the Quasiparticle-Phonon Model.

Values of modified Bethe–Bloch stopping power parameters for polysulfone extracted from stopping power measurements with light projectiles

Recent measurements of the stopping powers of polysulfone for 0.66–1.74 MeV protons and 1.04–3.20 MeV alpha particles have been analyzed in terms of the modified Bethe–Bloch theory in order to extract values of the parameters characterizing the formalism utilized. Resulting values of mean excitation energy ( I) and Barkas-effect parameter ( b), respectively, were 83.3 eV and 1.05 for proton data, and 81.1 eV and 1.38 for alpha particle data. The lower energy alpha particle data were included by employing a single effective charge parameter ( λ) evaluated at 1.63. The composite weighted value of mean excitation energy, 82.9 eV, lies some 6% above the additivity-based estimate, whereas the corresponding value of Barkas-effect parameter, 1.22, agrees quite well with the prescribed interval of 1.4±0.1.

Photoabsorption of the peroxide linkage defect in silicate glasses

First-principles quantum chemical techniques on cluster models have been used to investigate the photoabsorption of the peroxide linkage defect in silicate glasses. The effects of geometry, basis sets, and cluster size have been considered carefully to derive converged values for the low-lying excitation energies. The lowest singlet-to-singlet transition is a weak absorption at 5.5 eV. A stronger valence absorption occurs at 6.8 eV.

Experimental investigations of the nuclear level density by using heavy ion reactions

The transition of the level density parameter aoff from the low excitation energy value aoff=A/8 MeV−1 to the Fermi gas value aFG ∼ A/15 MeV−1 was discovered a few years ago studying particle spectra evaporated from hot compound systems of A∼ 160. A number of experiments have been recently performed to confirm the earlier findings and extend the investigation to other mass regions and to higher excitation energies. Furthermore, precision coincidence experiments have been done in the lead region in which evaporation residues are tagged by low energy gammarays. Those experiments open the possibility of a detailed study of the level densities in nuclei where the shell effects are important.

One-nucleon pickup reactions on 32S: Experimental results and shell-model calculations

The 32S( d, 3He) 31P and 32 S( 3 He,α) 31 S reactions have been investigated at incident energies of E d = 27 MeV and E 3 He = 25 MeV. The experimental values of excitation energies (0 ⩽ E x (MeV) ⩽ 8) have been compared with the predictions of a complete sd-shell space, shell-model calculation. Spectroscopic factors obtained for 22 levels of 31S through the DWBA analysis of the experimental angular distributions have also been compared with the shell-model predictions. In order to reconcile the experimental and shell-model predicted values of the spectroscopic factors, the geometrical parameters of the spin-orbit part of the transferred nucleon potential are required to be smaller than those of the central part as it was previously observed in studies of the one-proton ( 3He, d) stripping reaction. The experimental fragmentation of the 1d 5 2 and 2s 1 2 strengths is correctly reproduced by the shell-model calculations. Twenty pairs of levels were identified as mirror states in the 31S and 31P nuclei and the ambiguities concerning the J π -values of eleven 31S levels could be removed.

Synthesis of the porphyrin-fused porphyrin, [2]porphyracene

A novel porphyrin-fused porphyrin is formed by an oligomerization reaction of a (porphyrinato)nickel complex with TeCl4; the isolated compound, [2]porphyracene, was characterized by spectroscopic methods and direct observation using scanning tunnelling microscopy; the excitation energy value of 13460 cm–1 (743 nm) is the lowest value reported for porphyrin dimers.

25Mg(d,3He)24Nareaction at 29 MeV and a spectroscopic analysis of the levels of24Na

The ${}^{25}$Mg${(d,}^{3}$He)${}^{24}$Na reaction has been investigated at 29 MeV incident energy. Spectra were measured at ${\ensuremath{\theta}}_{\mathrm{lab}}=10\ifmmode^\circ\else\textdegree\fi{}$ and $18\ifmmode^\circ\else\textdegree\fi{}$. Observations using a split-pole magnetic spectrograph have been made of 56 levels of ${}^{24}$Na in the range of excitation energy between 0 and 7.3 MeV. Most of these have been identified with ${}^{24}$Na levels which have been previously observed by other techniques. From the ratios of the experimental as well as distorted-wave Born approximation (DWBA)-predicted cross sections at the two angles, the population through the pickup of an ${l}_{p}=1$ proton has been established (or confirmed) for the twelve levels at ${E}_{x}=3.372$, 3.745, 3.936, 4.524, 5.192, 5.250, 5.452, 5.846, 5.863, 6.905, 7.084, and 7.246 MeV. Spectroscopic factors were obtained from the comparison of the experimentally measured cross sections at the two angles with the DWBA-predicted cross sections. The experimental values of spectroscopic factors and excitation energies for positive-parity states were compared with the results of a recent, complete $\mathrm{sd}$-shell space, shell-model calculation. In conjunction with the results of various previous works, this comparison leads to the identification of 19 shell-model levels with experimental levels, and thus allows the removal of ambiguities existing in the current literature for the ${J}^{\ensuremath{\pi}}$ values of some ${}^{24}$Na states with ${E}_{x}l$3.7 MeV.

Photoreflectance spectroscopy with white light pump beam

Using a dual chopping scheme where both the pump beam and the probe beam are chopped, we show that it is possible to perform photoreflectance spectroscopy with a broadband white light source as the pump beam instead of a laser source. We show that although the signal strength is reduced by a factor of 1/π in the dual chopping scheme, it nevertheless has several advantages. A white light pump beam provides a wide range of excitation energy values, enabling one to characterize semiconductors of different band gaps spread over a wide energy range with a single modulation source. In the case of semiconductor heterostructures, simultaneous as well as selective excitation of different interfaces can be achieved easily. This technique is not plagued by the problem of background due to luminescence often encountered in low-temperature photoreflectance measurements. In this article, we present the details of this technique and demonstrate its usefulness by applying it to selected semiconductor heterostructure samples.

Structure of odd-odd Cu isotopes in the framework of the interacting boson-fermion-fermion model

In the present work, odd-odd ${}^{62,64,66}$Cu nuclei have been studied in the framework of the interacting boson-fermion-fermion model (IBFFM). Odd-odd Cu nuclei have been described with the parameters obtained from the IBM calculation for even Ni nuclei and the IBFM description of odd mass Cu and Ni nuclei. A simple delta interaction has been assumed between the odd neutron and the odd proton in the odd-odd nuclei. The calculated excitation energy values and the magnetic moments of odd Cu and Ni nuclei in the IBFM are compared to show the effectiveness of the parameters in explaining the low energy structure of these nuclei. Excitation energy spectra, magnetic moment and spectroscopic factors for the single-nucleon transfer reaction have been calculated for the odd-odd nuclei and are compared with the corresponding experimental values. The results seem to indicate the ability of the model to explain the low energy structure of odd-odd Cu nuclei.

A new implementation of the second-order polarization propagator approximation (SOPPA): The excitation spectra of benzene and naphthalene

We present a new implementation of the second-order polarization propagator approximation (SOPPA) using a direct linear transformation approach, in which the SOPPA equations are solved iteratively. This approach has two important advantages over its predecessors. First, the direct linear transformation allows for more efficient calculations for large two particle–two hole excitation manifolds. Second, the operation count for SOPPA is lowered by one order, to N5. As an application of the new implementation, we calculate the excitation energies and oscillator strengths of the lowest singlet and triplet transitions for benzene and naphthalene. The results compare well with experiment and CASPT2 values, calculated with identical basis sets and molecular geometries. This indicates that SOPPA can provide reliable values for excitation energies and response properties for relatively large molecular systems.

Influence of pressure on spectral intensities in a flowing nitrogen glow discharge

Intensity measurements on the second positive and first negative systems were made in a flowing dc nitrogen discharge in order to study the dependence on gas pressure. Different populating mechanisms for the states and together with different excitation energy values for these states account for the experimental results.

Dependence of intermediate mass fragment production on the reaction mechanism in light heavy-ion collisions at intermediate energy.

The same hot nuclear system (\ensuremath{\Sigma}Z=18) has been studied for two different entrance channels with reaction products detected in a forward array of scintillators: central collisions of $^{24}\mathrm{Mg}$ on a $^{12}\mathrm{C}$ target at 25A and 35A MeV and peripheral pickup reactions of $^{35}\mathrm{Cl}$ on a $^{197}\mathrm{Au}$ target at 43A MeV. The detection-efficiency-corrected charge distributions, multiplicity of charged particles and cross sections as a function of excitation energy are compared. The reaction mechanism is investigated, through comparison to simulations with statistical observables. The central reaction $^{24}\mathrm{Mg}$${+}^{12}$C at 35A MeV is well characterized by a dissipative binary collision scenario. Data at 25A MeV show less evidence of such dynamical characteristics. The intermediate-mass fragments (3\ensuremath{\le}Z\ensuremath{\le}8) production for each reaction is compared to model calculations for different values of excitation energy. The systems formed in the central collision at 25A MeV and the pickup reaction at 43A MeV show similar source characteristics, both statistically and in momentum space. However, the yields of the various exit channels, from evaporation and/or fission to multifragmentation and vaporization, differ for the two reactions. \textcopyright{} 1996 The American Physical Society.