Electronic structure of carbon trioxide and vibronic interactions involving Jahn-Teller states

The electronic structure of CO3 is characterized by equation-of-motion and coupled-cluster methods. C(2v) and D(3h) isomers are considered. Vertical excitation energies, transition dipoles, and the molecular orbital character of the excited states are presented for singlet and triplet manifolds. Ground-state equilibrium structures and frequencies are strongly affected by vibronic interactions with low-lying excited states. At D(3h) geometries, the vibronic interactions are enhanced by the Jahn-Teller character of the excited states. The curvature of the potential energy surface and the existence of the D(3h) minimum are very sensitive to the correlation treatment and the basis set. The correlation effects are stronger at D(3h), in agreement with a smaller HOMO-LUMO gap.     

Dyson orbitals for ionization from the ground and electronically excited states within equation-of-motion coupled-cluster formalism: theory, implementation, and examples

Implementation of Dyson orbitals for coupled-cluster and equation-of-motion coupled-cluster wave functions with single and double substitutions is described and demonstrated by examples. Both ionizations from the ground and electronically excited states are considered. Dyson orbitals are necessary for calculating electronic factors of angular distributions of photoelectrons, Compton profiles, electron momentum spectra, etc, and can be interpreted as states of the leaving electron. Formally, Dyson orbitals represent the overlap between an initial N-electron wave function and the N-1 electron wave function of the corresponding ionized system. For the ground state ionization, Dyson orbitals are often similar to the corresponding Hartree-Fock molecular orbitals (MOs); however, for ionization from electronically excited states Dyson orbitals include contributions from several MOs and their shapes are more complex. The theory is applied to calculating the Dyson orbitals for ionization of formaldehyde from the ground and electronically excited states. Partial-wave analysis is employed to compute the probabilities to find the ejected electron in different angular momentum states using the freestanding and Coulomb wave representations of the ionized electron. Rydberg states are shown to yield higher angular momentum electrons, as compared to valence states of the same symmetry. Likewise, faster photoelectrons are most likely to have higher angular momentum.     

Energy transfer studies in krypton-xenon mixtures excited in a cooled DC discharge

The VUV spectrum of gaseous mixtures of krypton with a small amount of xenon added was investigated in the range 115-200 nm. The mixtures were excited in a capillary DC discharge where the capillary could be cooled by using liquid nitrogen. The mixed molecule band around the XeI resonance line at nm and the mixed molecule continuum to the long wavelength side from the line were analysed. The band around nm was identified as transitions between a weakly bound excited state and the weakly bound ground state of XeKr molecules. When cooling the capillary wall, the appearance of the Xe₂ continuum was observed. The effect is ascribed to energy transfer between molecular states as a consequence of radiation trapping in the band around nm. The role of the mixed molecule in the formation of the VUV spectrum of the gas mixture is discussed and underlined. Received 12 May 1999 and Received in final form 27 August 1999     

Identification of structures in absorption spectrum of Kr-Xe gas mixtures close to the Xe resonance line at 146.96 nm

The origins of spectral structures that appear close to the Xe resonance line at 146.96 nm in absorption spectra of Kr gas with an admixture of Xe are discussed in this paper. It is shown that these structures can result from bound-bound and bound-free transitions in the Xe-Kr molecule between the ground state and the 1(³P₁) excited state, which both are weakly-bound. The depth of the excited state is estimated. An introduction of a hump on the 1(³P₁) state internuclear potential is suggested. Received 15 December 1999 and Received in final form 20 February 2000     

VUV spectra of krypton-xenon mixtures in a cooled DC-excited discharge

An experimental study was made of VUV spectra of a gas-discharge krypton plasma with a xenon impurity. The mixture pressure, the xenon impurity concentration, and the current were varied in ranges of 40–1000 hPa, 0.001–1%, and 10–50 mA, respectively. The heteronuclear XeKr dimers were shown to play a crucial role in the quenching of excitation energy of krypton dimers. The mechanism of transformation of the energy of excited krypton dimers in a low-temperature plasma of a binary krypton-xenon mixture is discussed.     

Concept of Plasma Heating and Current Drive Neutral Beam System for Fusion Neutron Source DEMO-FNS

Steady-state operation of a fusion neutron source (FNS) requires plasma heating and current drive by means of additional power delivered by neutral beams. Six neutral beam injectors (NBI) will provide the DEMO-FNS machine with additional heating power up to 30 MW, with neutral particle energy of 500 keV. NBI systems developed for ITER can serve as the prototype for DEMO-FNS, as both systems have similar ion source current, with accelerated beam power in ITER NBI (1MeV) being twice as large as in DEMOFNS. The paper describes the NBI system with account of its integration into DEMO-FNS tokamak complex.     

Experimental setup for ground-based measurements in preparing cosmic experiments to study nuclear planetology

An experimental laboratory setup combining various gamma spectrometers and neutron generators that is intended for operating at the experimental nuclear-planetology facility deployed at the Joint Institute for Nuclear Research (Dubna, Russia) in order to perform physical calibrations of active gamma and neutron spectrometers is described.     

Magnetic properties, magnetoresistance, and Raman spectra of CuV x Cr1 − x S2

The results of investigations of the magnetic and Raman spectra, magnetic properties, and magnetoresistance of vanadium-substituted chromium copper disulfides CuV _x Cr_{1 ? x} S₂ (x = 0.1) are presented.     

Formation, electronic structure, and stability of film nanophases of transition metals on silicon

This paper is devoted to the study of the morphology, growth, electronic structure, and stability of ultrathin (0.03–3 nm) Co and Fe films on the Si(111) and Si(100) surfaces using Auger-electron spectroscopy, electron-energy loss spectrometry, low-energy electron diffraction, and atomic-force microscopy. It is shown that layer-by-layer growth of the metal with the formation of the film nanophase and the segregation of a submonolayer amount of Si on the film’s nanophase surface occurs during the process of layer-by layer growth of Co and Fe on Si(111)-7 × 7 and Si(100)-2 × 1 at room temperature after the growth of two-dimensional metal phases (the surface phase, the monolayer, and two metal monolayers). After these stages, the formation and growth of the bulk’s metal phase with the dissolution of silicon segregated before occur. It is shown that the upper layers of Si adjoining the surface phase, the monolayer, and two Co and Fe monolayers have respectively three different densities of the electron plasma that are higher than the density of the electron plasma in the volume of the silicon substrate. The nonmonotonous character of the morphological and chemical stability of Fe films with quantum-size thicknesses on Si(100) is discovered. After annealing, the film is first smooth, then it is nonuniform across its thickness; afterwards it is again smooth and then nonuniform across its thickness. In this case, the metal phase, different Fe silicides, and the bulk’s metal phase form successively in Fe films on Si(100) after annealing.     

Quantitative determination of n-alkanethiols in air and in a blended gas mixture of methane with air by gas chromatography/differential mobility spectrometry

Mixtures of n-alkanethiols, in solution with equi-molar amounts from 0.5 to 360 ng per compound, were determined using gas chromatography (GC) with a differential mobility spectrometer, operated with a flow of air at ambient pressure, as the GC detector. A homologous series of n-alkanethiols with carbon number from two to six showed baseline resolution in the GC separation and positive and negative ion chromatograms were produced simultaneously for the alkanethiols. Differential mobility spectra showed compensation voltages characteristic of each alkanethiol and plots of ion intensity, retention time, and compensation voltage yield contour plots illustrating the second dimension of analytical selectivity provided by the detector. Another yet undeveloped dimension of analytical information was found in the dependence of mobility coefficients on electric field. Mass-analysis of ions from thiols showed a hydrogen abstracted ion, protonated monomers, and proton bound dimers. Linear ranges were narrow and the minimum detectable limits were ~1 ng. Response in positive polarity provided a ten-fold improvement in detection limits though spectra were more complex than for negative ions. In a methane-rich air atmosphere, intended to simulate ambient air or the detection of leaks from natural gas pipelines, the response to thiols with negative ions was not degraded by the methane up to 50% v/v, the highest level tested.