Open-shell Structure Research Articles

THE STRUCTURE OF REACTED METAL CLUSTERS: PHOTOELECTRON SPECTRA OF ${\rm{Pt}}_n^-$ CLUSTERS REACTED WITH CO

[Formula: see text] clusters produced by a laser-vaporization source are reacted with CO. The various reaction products [Formula: see text] are studied systematically using photoelectron spectroscopy of negatively charged clusters. First results are interpreted in terms of the Blyholder model. The spectra indicate an open electronic shell structure of the unsaturated and a closed shell structure of the saturated Pt carbonyls. For [Formula: see text] emission from the 2π/5d hybrid orbital is directly observed. The assignment is supported by the measured vibrational fine structure.

Low-energy H+, He+, N+, O+, and Ne+ scattering from metal and ionic-compound surfaces: Neutralization and electronic excitation.

Neutralization and electronic excitation during low-energy ion-surface scattering have been investigated from a combination of experiments and molecular-orbital energy calculations based on the discrete variational X\ensuremath{\alpha} method. It is found that a variety of electronic transitions are mediated by the molecular orbitals during the violent collision or the short-lived chemisorption state of the ions, which may not be inferred from the atomic orbitals of the isolated projectiles. The rare-gas ions, such as ${\mathrm{He}}^{+}$ and ${\mathrm{Ne}}^{+}$, capture a valence electron mainly via the Auger neutralization process, whereas resonant tunneling can also play an important role in neutralization of the reactive ions (${\mathrm{H}}^{+}$, ${\mathrm{N}}^{+}$, ${\mathrm{O}}^{+}$). The occurrence of resonant tunneling is related to the open-shell structure of the reactive ions. The probability for resonance neutralization is sensitively dependent upon the nature of the valence band (band effect) and is largely enhanced at the metal surface relative to the ionic-compound surface. The valence-band electron can be excited in scattering of reactive ions as a sequence of neutralization/ionization along the promoted antibonding molecular orbital. In scattering of the rare-gas ions, not only the valence electron but also the semicore electron can be excited for specific ion-target combinations in which sufficient promotion of the antibonding molecular orbital can take place during collision.

Covalent container compound: Empty, endohedral, and exohedral C28 complexes.

Results from quasidynamical local-density simulations on a small fullerene complex (C 28 ), three endohedral complexes (C 28 αC, C 28 αZr, and C 28 αTi), a C atom bound to the corner of the C 28 molecule, and C 28 H 4 are presented. This molecule forms spontaneously from a 29-atom diamond crystallite and, under proper circumstancse, is a covalent container compound. Upon encapsulation of a Zr atom, 12.6 eV of energy is liberated leading to an unreactive closed-shell C 28 αZr molecule. The open-shell structure of the empty molecule leads to a reactive yet relatively stable building block which might be useful for synthesis of new metastable forms of carbon-based material

The self-consistent spheroidal jellium model of open-shell monovalent metal clusters

Recently, we have proposed a microscopic model, describing the properties of open-shell, Jahn-Teller deformed monovalent-metal clusters [1]. The model is based on the self-consistent ground-state calculation, allowing the spheroidal (axial) deformation of the ionic jellium background, driven by the open-shell valence electron structure. The ground state electronic properties of such clusters are further investigated and compared to recent experimental data: ionization potentials, electron affinities and binding energies of neutral monomers to cationic clusters [2].

Auger transitions in open-shell configurations withns (n=4,5,6)outer electron

Nonradiative transitions in nonclosed-shell atoms K ($Z=19$), Ag ($Z=47$), and Au ($Z=79$) with $\mathrm{ns} (n=4,5,6)$ outer electron are studied by comparing the calculated transition rates with the experimental ones. Auger transitions involving the next inner shell show clear fine structure due to the coupling of the outer $\mathrm{ns}$ electron with the holes producted in the Auger decay. The observed intensity distribution is found to be reproduced reasonably well with the calculations which explicitly take into account the open-shell structure.

Two-body propagators with dynamic effective interactions in a many-fermion medium: II. s-Channel

In open-shell nuclear structure calculations collective excitations of the closed-shell core play an important role. When the energies of these excitations are comparable to the spread of energies in the model space a dynamic treatment of the core states is essential. In a Green function formulation dynamic core states, represented by particle-hole phonons, are included in the effective interaction of the s-channel integral equation for the fourfermion vertex function Γ. The solution of the equation is obtained analytically and from it the s-channel two-body propagator K is calculated. The structure of the propagator K reveals that, in addition to poles corresponding to the normal shell model states, many new poles of K are obtained. These correspond to two-particle- n-phonon configurations. Furthermore, it is shown that, due to the phonons, correlations of the ground state are induced in the calculation of the propagator K. The difference between these correlations and the well-known particle-particle-RPA correlations also included in the formalism is pointed out. The expressions derived can easily be handled numerically. In the calculations the physical states of single-particle and single-hole nuclei can be incorporated by an appropriate dressing of the single-fermion Green function.

Electronic structure and MnO

SCF calculations have been performed in order to get information upon the ground and lowest excited states of manganese monoxide MnO and to study the bonding mechanism in this molecule. The ground state is found to be a 6Σ + state and configuration interaction calculations indicate that it is represented for more than 60% by the (8σ 2 9σ 4π 2 16 2) configuration. In this energy level, the closed shell 8σ orbital is the bonding orbital and the three open-shell orbitals are strongly localized on 3d(Mn). This open-shell structure on manganese 3d induces interesting analogies between the molecule and the manganese atom. SCF potential curves have been plotted in a diagram. The lowest excited states are found to be the observed A 6Σ + and a 6II state. The A 6Σ + - X 6 X 6Σ + transition is the charge-transfer 8σ « 10σ excitation. Rearrangements of orbitals in the excited states in order to maintain a Mn + (3d 5 4s) − O −(2p 5) gross structure are pointed out. The results are compared to those of earlier semi-empirical studies and found to be essentially different.

A suggested mechanism for the visible chemiluminescence observed in gas phase aluminum oxidation

A reaction mechanism that generates the excited ( A 2 Π) and/or lowest-lying 4 Σ + and 4 Π states of AlO is suggested as the source of the visible chemiluminescence often observed in the gas phase oxidation of aluminum. Data from upper atmospheric chemical release experiments utilizing aluminized grenades, aluminized burners, and trimethylaluminum appear to be inconsistent with previously proposed mechanisms, but can be reasonably accounted for by AlO ∗ pumping reactions of molecules containing loosely bound aluminum atoms with atomic oxygen. The prototype reaction Al 2 + O and Al + O 3 are discussed in some detail, in terms of the correlation of reactant and product states. According to the “electron-jump” model, the formation of excited AlO ∗ with high quantum efficiency can be expected as a consequence of the open shell structure of the aluminum oxide molecule.

Semi-empirical Unrestricted SCF-MO Treatment for Valence Electron Systems. I. Application to Small Doublet Radicals

Abstract A semi-empirical SCF method for valence electron systems including a differential overlap previously proposed by the present authors is here extended to molecules with an open-shell structure. The unrestricted Hartree-Fock method is applied, and the one-centre and part of two-centre σ-π-type exchange repulsion integrals, playing an essential role in spin-density calculations, are included in the calculations. The calculated spin densities are divided into the mechanistic (spin-polarization and spin-delocalization) contributions. The spin-polarization mechanism is shown to be important even in cases where the spin delocalization mechanism has usually been considered to be dominant (e.g., ethyl and vinyl radicals). The calculated spin densities of π-electron radicals (methyl, ethyl, allyl, and trans-butadienyl anion radicals) and of σ-electron radicals (vinyl, formyl, NO2, CO2−, CN) are discussed. Their hfs constants and mechanistic contributions are calculated; for the methyl and vinyl radicals these are shown to be strongly angular-dependent. The calculated potential curve and the hfs constants of the vinyl radical lead to the CCHa angle, θ\simeq135°; furthermore, the Hα and Cβ hfs constants are shown to be negative. Generally, the calculated proton hfs constants agree satisfactorily with the experimental data and with other calculations except in the case of the formyl radical. The atomic dipoles of some σ-electron radicals are calculated, and some interesting features common to all the σ-electron radicals studied are found.