V. K. Dolmatov

The filling of shells in compressed atoms

The energy spectra of ground-state, ionized and excited multielectron atoms and ions of the 3d and 4d periods of the periodic table centred in impenetrable spherical confinement are detailed using Hartree-Fock configuration average calculations. It is shown explicitly for the first time that, owing to modifications in 3d and 4d orbital collapse, the filling of shells for the confined transition sequences becomes more regular than for free atoms with increasing confinement pressure, that s-d competition disappears, and that, for d-excited states, the crossings between inner-shell excited states and the double-ionization thresholds are altered. In general, the periodic table for confined (compressed) atoms can differ from that for free atoms. The importance of these findings for different branches of basic and applied physics and chemistry is indicated.

A unique situation for an endohedral metallofullerene

This letter demonstrates for the first time that an endohedral environment, such as the bucky-ball C60, can produce a significant redistribution of oscillator strengths in endohedrally trapped atoms, making the dominant transitions no longer superior but inferior, and also making electron correlations in such atoms act in an opposite way to free atoms. This is exemplified by calculations of the oscillator strengths and photoionization cross sections of the Ca atom trapped inside C60. Also, while photoionization cross sections can undergo dramatic changes on confinement, the photoelectron angular asymmetry parameter n can, in contrast to natural expectation, remain largely unchanged. The random-phase approximation with exchange was employed. We believe these are the first calculations of electron correlations for confined atomic species.

Controlled strong non-dipole effects in photoionization of confined atoms

It is demonstrated that non-dipole effects in low energy photoionization of atoms surrounded by a repulsive semi-transparent potential can be increased by many orders of magnitude due to virtual levels occuring in the spectra of photoelectrons as a result of confinement. The strengths, widths and positions of such resonances in non-dipole channels can be controlled by altering the characteristics of the confining potential, and under certain circumstances can be so large that treating quadrupole transitions as a perturbation breaks down, even for photon energies as low as tens of eV. Our conclusions have relevance to the interpretation of non-dipole photoemission spectra from solids, molecules, atoms trapped inside fullerene molecules, quantum dots, etc.

MULTICENTERED THEORY OF MOLECULAR PHOTOIONIZATION

A new theory for near-threshold photoionization of inner electrons of atoms confined in multicentered atomic formations, e.g. molecules or clusters, is developed. The formulas for fixed-in-space molecules have been derived. The interaction of the photoelectron in the continuum with atoms that surround the atom being ionized, is replaced by the suitable boundary conditions imposed on the photoelectron wave function at the location of nuclei of these atoms in the molecule. The general formulas derived are used to calculate photoelectron angular distributions of diatomic molecules. The calculated data are in qualitative agreement with experimental data and results of other calculations.

On the dependence of inner-shell photoionization on the outer-shell structure of

Since inner-shell photoionization cross sections in the region of purely inner-shell-to-inner-shell resonances are generally insensitive to the state of excitation or ionization of outer electrons, the most sensitive comparison between theory and experiment for photoionization cross sections of excited or ionized atoms is in the region of inner-shell-to-outer-shell resonance transitions. The experimental 3p absorption cross section of is compared with theory as an example.

“Reading” the photoelectron β -parameter spectrum in a resonance region

The behavior of the dipole photoelectron angular distribution parameter {beta}{sub nl}({omega}) in the vicinity of autoionizing resonances is discussed. It is shown that from this behavior, surprisingly, many photoionization parameters that cannot be measured experimentally can be extracted. These are the energy positions and ordering of autoionizing resonance minima in the partial photoionization cross sections {sigma}{sub l+1} and {sigma}{sub l-1}, the energies at which these two cross sections intersect, and signs and magnitudes of the cos({delta}{sub l+1}-{delta}{sub l-1}) ({delta}{sub l{+-}}{sub 1} being the phase shifts of the dipole photoionization amplitudes D{sub l{+-}}{sub 1}, respectively) through the autoionizing resonance energy region. Based on this, a deeper interpretation of such effects as the width-narrowing, width-fluctuating, and q-reversal in the {beta}{sub nl} parameter spectrum in the autoionizing resonance energy region is given. As an example, calculated data for partial photoionization cross sections {sigma}{sub 3d{r_reversible}}{sub f} and {sigma}{sub 3d{r_reversible}}{sub p}, and {beta}{sub 3d} parameters for 3d photoelectrons from Cr{sup +} are presented.

Confined Atoms: A New Path Towards Controlled Orbital Collapse

Atomic orbital collapse, which arises as a result of centrifugal barrier phenomena in many-electron atoms is a well-established effect [1], and has been invoked to account for anomalies in the filling of the d and f transition sequences [2], for the presence of giant resonances in many of their spectra [3], as well as for critical phenomena which appear as perturbations of Rydberg series [4].