Determination Of Excitation Energy Research Articles

The two-electron terms of the no-pair Hamiltonian

New programs have been developed which enable us to calculate the two-electron terms of the no-pair Hamiltonian. We present all-electron calculations for the atoms Ag and Au with nonrelativistic and relativistic Hamiltonians. Self-consistent field ground state energies and orbital energies are reported. The configuration-interaction method is used to determine excitation energies, ionization potentials, and electron affinities. By comparing the results for different operators the effect of the relativistic correction of the two-electron integrals is investigated.

Excitation energies calculated with parameter-free exchange potential in the density functional theory

The parameter-free exchange potential of Gaspar (1974) has been applied to determine excitation energies of Na and K atoms. The calculations have been done with the fractional-occupation approach of the density functional theory formulated by Gross et al. (1988).

Spin—orbit effects in the Br atom in the framework of the no-pair theory

New programs have been developed which enable us to calculate the two-electron terms of the no-pair Hamiltonian. We present all-electron calculations for the Br atom with non-relativistic and relativistic Hamiltonians. The MRD-CI method is used to determine excitation energies from the 2P u ground state to the first excited states 4P g and 2P g. The zero-field splitting of the ground state is investigated by means of first-order perturbation theory. Non-relativistic and relativistic spin—orbit Hamiltonians are applied in the perturbation calculations, whereby the spin-free CI wavefunctions have been used as zero-order solutions of the unperturbed system. By comparing the different results for the spin—orbit matrix elements, we are able to separate effects arising from the relativistic wavefunction and effects caused by the relativistic spin—orbit Hamiltonian.

States of 25Al between 6 and 8 MeV

Polarized protons were scattered from 24Mg in 20 keV steps at laboratory energies between 4 and 6 MeV, corresponding to excitation energies in 25Al between 6 and 8 MeV. Cross sections and analyzing powers were measured at 14 angles for elastic scattering and for inelastic scattering to the first excited state in 24Mg. A phase-shift analysis was done for the elastic scattering data. The energy dependences of the extracted phase shifts were used to determine excitation energies, spins, parities and widths of levels of 25Al.

A surface enhanced hyper-Raman scattering study of pyridine adsorbed onto silver: Experiment and theory

This paper presents a combined experimental and theoretical study of the hyper-Raman spectrum of pyridine adsorbed onto roughened silver electrodes. The surface enhanced hyper-Raman spectra (SEHRS) were measured using a focused cw mode-locked Nd:YAG laser with a peak power density of approximately 107 W/cm2 . Dominant bands in the pyridine spectra are the same (totally symmetric) bands as have been seen in the corresponding Raman (SERS) spectrum, although the relative intensities are different. To interpret these spectra, we present a semiempirical molecular orbital method for determining excitation energies, polarizability derivatives, and hyperpolarizability derivatives that is based on the π-electron Pariser–Parr–Pople (PPP) method. An empirical molecular force field is used to derive vibrational information, and the accuracy of the spectra is assessed by comparison with normal Raman spectra for liquid pyridine and with SERS spectra. The resulting SEHRS spectra are in good agreement with the measured spectra, particularly with respect to the intensity changes in the dominant lines in going from SERS to SEHRS. In addition, the theoretical/experimental comparisons indicate that SEHRS is more sensitive to adsorbate orientation than is SERS since the nontotally symmetric modes are predicted to be comparable in SEHRS (but not SERS) intensity to the totally symmetric modes for orientations other than perpendicular. Most important, a comparison of theoretical and experimental SEHRS/SERS ratios suggests that the enhancement factor associated with SEHRS is on the order of 1013 which is much larger than the 106 enhancement seen for SERS.

Excitation energies in Be: A comparison of multiconfigurational linear response and full configuration interaction calculations

Using a 〈9s9p5d〉 contracted GTO basis we have calculated low-lying excitation energies of singlet and triplet symmetry for the Be atom using Δfull CI, ΔCI(1s) with double occupancy in the 1s orbital, multiconfiguration linear response (MCLR), and ΔMCSCF approaches. The Δfull CI results agree very closely with the experimental excitation energies except for higher excitations where obvious basis set defects occur. The MCLR calculations shows that with an adequately chosen MCSCF reference state the MCLR calculation is capable of mimicking the Δfull CI results. The MCLR results are closer to the Δfull CI results than the ΔCI(1s). The ΔMCSCF excitation energies show that this approach can only be used with extreme care to determine excitation energies.

Relativistic Random-Phase Approximation

The relativistic random phase approximation RRPA is developed from linearized time-dependent Hartree-Fock theory. Applications of the resulting relativistic many-body equations to determine excitation energies and oscillator strengths along the He, Be, Mg, Zn and Ne isoelectronic sequences are discussed and compared with other recent experimental and theoretical work. The multi-channel RRPA treatment of photoionization is described and applications are given to total cross sections, branching ratios, angular distributions and to autoionizing resonances.

Determination of excitation energies and transition moments in a second order polarization propagator approach. Application to the Be atom and the CH+ molecule

AbstractExcitation energies and transition moments have been determined from a second order polarization propagator and the effect of including energy shifted denominators has been investigated. Results for Be and CH+ show a change of 2–5% for the transition moments and of 0–20% for the singlet excitation energies in a second order approach compared to a first order (time‐dependent Hartree‐Fock) approximation. Both Be and CH+ are triplet unstable in the time‐dependent Hartree‐Fock approximation. The triplet instability is removed for Be but not for CH+ in a second order polarization propagator approach.

High-resolution time-of-flight system for precise measurement of excitation energies and Q-values

A time-of-flight system has been installed for the measurement of accelerator beam energies with an absolute accuracy of 1.5 : 10 5 as proved by determining excitation energies in 60Ni. The first T= 3 2 resonance in 12C(p,p) 12C was measured at E p=14230.75±0. 20 keV.

A Modified quasiparticle Model

Abstract By use of the quasiparticle-quasihole space as model space, a model is established in order to determine excitation energies and transition probabilities of atomic nuclei. The equations derived show a remarkable correspondence to those in Migdal’s quasiparticle theory. The validity of the quasiparticle hypothesis, which is fundamental in Migdal’s theory, is not a necessary condition for a weak dependency of the effective interaction. This energy dependency is also independent of the choice of the one particle basis.

On determining excitation energies from the poles of green functions

The method of determining the low-lying excitation energies of a system by locating the poles of the Fourier transform of the single-particle Green's function for the system is shown to lead to incorrect results under certain circumstances. A system represented by a certain generalized Hamiltonian is shown as an example; the Green's function method for this system leads to several spurious energy levels. It is shown that the Green's function method is particularly inaccurate in perturbation theoretical approaches.

On collective levels of non-spherical nuclei

The β- and γ-vibrational levels in non-spherical nuclei are interpreted microscopically. Using the method of approximate second quantization an equation is obtained for determining excitation energies of these levels. Electro-magnetic transition probabilities are also calculated for them. The theory is compared with experimental data.

Accurate Determination of Excitation Energy by Electron Impact

Accurate Determination of Excitation Energy by Electron Impact