Classification of Low-Lying States of Two-Dimensional Three-Electron Systems

The Schr?dinger equation of a two-dimensional three-electron quantum dot has been solved accurately. Features of the structures of low-lying states have been extracted from the wave functions. The states are classified according to their geometric characters and their internal modes of motion. The effect of symmetry is emphasized. Rotation bands have been found. Received August 16, 1995; revised November 4, 1996; accepted for publication November 25, 1996     

Analysis of the Structure of Low-Lying States of Four-Boson Systems Based on Symmetry

The structure of inherent nodal surfaces of four-boson systems has been investigated. The most probable structures for each low-lying state have been found. A number of predictions on the structures of individual states and on the systematics of the spectra have been found. Received July 18, 1996; revised March 15, 1997; accepted in final form September 30, 1997     

EC/β+ decay of six medium-heavy nuclei

Previous experimental results of (EC+β+) decay for the medium-heavy nuclei reported by our group since 1996, including 153Er, 157Yb, 209Fr, 128Ce, 130Ce, and 128Pr have been briefly summarized. The observed low-lying states in their daughter nuclei have been reviewed in a systematic way and compared with different model calculations. Finally, some questions have been put forward for further study and discussion.     

The photoproton decay of 27Al

Photoproton spectra from ²⁷Al were measured from 14.8 to 27.6 MeV excitation energy in 400 keV steps. From these, high resolution photoproton cross sections to low-lying states of the residual ²⁶Mg nucleus were deduced. The large integrated cross sections to these states justify the interpretation of the de-excitation γ-ray measurements which consistently indicate strong population of low-lying residual states following photodisintegration. Further, the results are discussed with reference to the particle-hole model. By examination of the microscopic configurations of the possible GDR states an explanation is proposed for the differences in the cross sections to various residual states. Finally, the results are compared with spectroscopic factors determined from pickup reactions on ²⁷Al.     

Low-lying excited states of quantum antiferromagnets on a triangular lattice

We study low-lying states of theXY and Heisenberg antiferromagnets on a triangular lattice to clarify whether spontaneous symmetry breaking occurs atT=0 in the thermodynamic limit. Approximate forms of low-lying states are proposed, in which degrees of freedom of the sublattice magnetization and of the chirality are separated. These approximate states have a long-range order and twofold structures. It is shown that low-lying states can be accurately described with the present approximation. It has been argued that low-lying states play an important role in symmetry breaking. With the help of this approximation, we discuss the contribution of low-lying states to symmetry breaking of two types, namely creation of the spontaneous sublattice magnetization and the spontaneous chirality. Furthermore, to show evidence for the occurrence of symmetry breaking, we numerically study the low-lying states of finite systems of theXY and Heisenberg antiferromagnets. It is found that the necessary conditions for the symmetry breaking to occur are satisfied in these models.     

Effect of the group IV elements on the Π anion and cation states of thiophene and furan determined by means of ETS and UPS

The electron-transmission and He(I) photoelectron spectra of Si(CH₃)₃, Sn(CH₃)₃ and CH₂Si(CH₃)₃ derivatives of thiophene and furan have been recorded. The first two substituents perturb the energies of the outer filled π orbitals and of the empty π* orbitals in opposite directions, causing a reduction of the HOMO/LUMO energy separation. The stabilization experienced by the π* MO's depends on their wavefunction coefficients at the site of substitution, and is attributed to interaction with low-lying empty orbitals of the substituent groups. The relatively small size (～ 0.4 eV) of this effect on the unoccupied ring MO's suggests that it should not appreciably affect the energy of the filled MO's.The strong conjugation between the π* unoccupied orbital of the nitro group and those of thiophene has also been investigated.     

Electronic states and spectroscopic properties of MgH in absence and presence of spin–orbit coupling − a configuration interaction study

Electronic spectrum of astrophysically important molecule magnesium hydride (MgH) has been studied using configuration interaction methodology excluding and including spin–orbit coupling. Potential energy curves of several spin-independent (Λ?S) electronic states have been constructed and spectroscopic constants of low-lying bound Λ?S states within 8.2 eV of term energy are reported in the first stage of calculations. The X²Σ⁺ is identified as the ground state in the Λ?S level. In the subsequent stage, the spin–orbit interaction has been incorporated and its effects on the potential energy curves and spectroscopic features of different electronic states of the species have been investigated. The X²Σ⁺_1/2 is identified as the spin–orbit (Ω) ground state of the species. Transition moments of several dipole-allowed transitions are computed in both the stages and radiative lifetimes of the corresponding excited states are computed. Electric dipole moments (µ) for a number of low-lying bound Λ?S states as well as several low-lying Ω-states are also calculated in the present study.     

The Modes of Internal Motion and Classification of a Three-Electron State in Quantum Dots

The physics underlying the low-lying states of a three-electron system (S = 1/2, L = 0 to 6) confined in a two-dimensional quantum dot by a parabolic potential has been investigated. The modes ofinternal motion in the low-lying states have been identified based on an analysis of the inherent nodal surfaces originating from the quantum mechanical symmetry. Furthermore, a classification for the low-lying states has been proposed.     

Generating an Inversion on a Nuclear Transition – Photopumping of 103Rh

Quite a number of proposals for a gamma-ray laser have been made over the years. One first step on the way to a gamma-ray laser is an inversion between nuclear states. For the natural isotope ¹⁰³Rh we have the favorable condition that there are two low-lying nuclear levels at energies of 357 keV and 295 keV with lifetimes of 107 ps and 9.7 ps, respectively. With two Nuclear Resonance Fluorescence (NRF) measurements the population of these low-lying levels via feeding from higher-lying levels was investigated. Altogether 26 higher-lying nuclear levels that show a branching to one or even both interesting low-lying levels have been found. Summing over all contributions from these feeding levels this results in a population inversion between the levels at 357 keV and 295 keV of ¹⁰³Rh. This revised version was published online in August 2006 with corrections to the Cover Date.     

A theoretical study of potential energy curves and spectroscopic constants of VC

Potential energy curves for the various low-lying electronic states of VC have been studied using complete active space multi-configuration self-consistent field (CASMCSCF) followed by first-order and multireference singles and doubles configuration interaction (FOCI, MRSDCI) calculations. The MRSDCI calculations included up to 6 million configurations. Two very low-lying electronic states are found as candidates for the ground state of VC, namely a high spin state ⁴Δ and a low-spin ²Δ state, which is favoured at higher levels. A number of low-lying excited electronic states of VC are predicted, which are yet to be observed. The low-lying electronic states of VC are found to be ionic as inferred from the dipole moments and the charge density calculations. Electron donation and the back-donation process are suggested to be operative in the V-C bond formation.     

Study of phase separation in Ti-Co-N thin films on silicon substrate

73 Co₂₇ and Ti₇₃Co₂₇- N during thermal annealing has been studied by SIMS, AES and XRD methods. It has been shown that in case of Ti₇₃Co₂₇ the CoSi₂ layer was not formed and the formation of ternary silicide compounds CoTiSi and Co₃Ti₂Si took place. At the same time in case of Ti₇₃Co₂₇- N the bottom layer CoSi₂ and the upper layer based on TiN were formed. The interaction behaviour has been found to depend on nitrogen concentration in initial film. For high amount of nitrogen the diffusion of Si atoms into upper layer and Si₃N₄ phase formation were observed. The possible variants of solid-phase interaction between silicon and the alloys containing intermetallic compounds and influence of nitrogen on this process are discussed. Received: 25 September 1996 / Accepted: 11 October 1996     

Nuclear structure of <Superscript>76</Superscript>Ge from proton-neutron interacting boson model calculations

The properties of low-lying states in ⁷⁶Ge, especially the characteristics of the mixed-symmetry states, have been investigated within the neutron-proton interacting boson model (IBM-2). By considering the relative energy of d proton boson to be different from that of neutron boson, the low-lying positive parity levels and M1, E2 transition strengths have been calculated. The IBM-2 calculated results are in good agreement with the experimental data. Particularly, the mixed-symmetry states have been reproduced quite well. The calculation and systematic analysis demonstrated that the collective character of ⁷⁶Ge lies closest to the SU*_πv(3), with some possible O_πv(6) dynamic symmetry in IBM-2 viewpoint.     

On the interpretation of weak intensity features in the low-lying valence level photoemission spectra of selected aromatic amines: diphenylamine,carbazole and N-alkyl substituted analogs

Existing valence level photoemission spectra of diphenylamine, carbazole and their N-alkyl substituted analogs exhibit characteristics unusual of “large” organic molecules in that well-resolved weak intensity features appear within ~ 3.0 eV of the photoionization threshold. The electronic structure of low-lying radical cation states of the title compounds were calculated self-consistently within the open-shell RHF CNDO/S(CI) formalism to address the nature of the apparent low energy intensity reductions. The π-electron doublet states which correlate with the experimental features in question are found to undergo a considerable loss of primary hole-state (Koopmans') character due to configuration interaction with higher-lying virtual orbital (non-Koopmans') excitations. The percentage of Koopmans' character contained in each final-state yields intensity profiles closely paralleling the experimental distributions.     

Deduction of the quantum numbers of low-lying states of the (e+e+e−e−) system from symmetry consideration

The features of the low-lying spectrum and the complete set of quantum numbers of each of the low-lying states of a (e⁺e⁺e⁻e⁻) system have been deduced based on symmetry.     

A study of the nuclear response function

We examine the excitation properties of spherical nuclei in the Random Phase Approximation using the Green's function method. The calculations are done with interactions of the Skyrme type for nuclei from ¹⁶O to ²⁰⁸Pb. Different Skyrme interactions can have the same predictions for ground state Hartree-Fock properties, but give quite different predictions for the dynamic response. Our calculations favor a mild velocity-dependence in the interaction, such as given by Skyrme I. The level of agreement with empirical properties is as follows: energies of low-lying states, ≈25%; positions of giant resonances, ≈10%; transition rates of low states, factor of 2 typical. Inelastic scattering of electrons is reasonably accounted for by the model, but nucleon inelastic scattering has difficulties with the noncollective strength.     

Generalized Heisenberg theory of turbulence

The properties of the low-lying excited states of⁵³Mn have been investigated in the framework of the intermediate-coupling unified nuclear model. In the present calculations, it was assumed that three holes in the 1f _7/2 proton shell, which undergo excitations, are coupled to the quadrupole vibrations of the doubly even core. Energy levels and electromagnetic properties have been calculated. In most cases, the results are found to be in good agreement with the experimentally observed values for the low-lying excited states in⁵³Mn. The results are also compared with those obtained from other models.     

Low-lying Gamow-Teller transitions in spherical nuclei

The Pyatov Method has been used to study the low-lying Gamow-Teller transitions in the mass region of 98 ⩽ A ⩽ 130. The eigenvalues and eigenfunctions of the total Hamiltonian have been solved within the framework of proton-neutron quasiparticle random-phase approximation. The low-lying β decay log(ft) values have been calculated for the nuclei under consideration.     

A study of the (3He,n) reaction on isotopes of tin

The (³He, n) reaction has been studied on^{112,116,118,120,124}Sn at 25.4 MeV. Angular distributions were measured over the range 0°–25° and the results compared with predictions of zero-range DWBA calculations. In addition to the around-state transitions, L = 0 transitions were also observed to low-lying states in every case. Simple two component wave functions, as well as those obtained from a more sophisticated pairing model, are compared with the data in order to explain the appearance of the anomalously low-lying excited 0⁺ states observed. L = 2 transitions were observed to low-lying 2⁺ states, but the strength of these transitions was much less than expected from the systematics of (t, p) results for N = 50 nuclei.     

Prediction of large corrections to Koopman's theorem and the ab initio vertical potentials of HOCl,FOCl and Cl2O

A low-lying σ virtual orbital (together with an occupied σ orbital with not too low an energy) is predicted to lead to large corrections to Koopmans' vertical ionization potentials for π-ionizations, and vice versa. The basis for such a “rule of thumb” is clarified. The prediction is shown to work consistently for our earlier calculations on F₂O and HOF and for the present results on Cl₂O, HOCl and FOCl.