Table of contents

New regularities are reported for valence-shell autoionizing Rydbergs decaying to a continuous spectrum of the valence subshell of free metal atoms and ions with semifilled subshells: , , and . We predict an extreme narrowing for the autoionizing Rydbergs in the atoms and ions with a ground-state valence-shell configuration. In contrast, incomparably broader Rydbergs occur in both atoms and ions with a ground configuration , or in metastable atoms and ions whose electron configuration is . We also predict a drastic difference between the Rydberg profiles in partial and photoionization cross sections of the atoms and ions with a closed valence subshell (arrows and show the two possible spin orientations for the ejected photoelectrons). The regularities disappear for atoms and ions with other than an semifilled subshell. The research is performed within both the `spin-polarized' Hartree - Fock approach and the `spin-polarized' random-phase approximation with exchange.

The results of many-body calculations for outer 4s-subshell photodetachment of the negative ion are presented. The 4s cross section reveals a near-threshold strong maximum, which may be attributed to the presence of a quasi-bound `4p' state in the continuum. It is shown that the resonance depends strongly on core-polarization effects. The dynamical polarization interaction between the atomic core and the extra electron have been taken into account within the Dyson equation method. The latter was used to bind the extra electron to a neutral Cr atom in the 4s state, to obtain its energy and wavefunction (the calculated energy is 0.782 eV, the electron affinity is 0.667 eV) and to correct the photoelectron wavefunctions. The wavefunctions thus obtained are used for the photodetachment cross section calculations.

We have simulated the evaporative cooling of trapped atoms using a very efficient method originally introduced for the study of molecular gas dynamics. This straightforward and intuitive method allows the dynamics of the evaporative cooling process to be studied and requires fewer simplifications and assumptions than other methods. In particular, the method is not restricted to distributions close to equilibrium and therefore it can model accurately rapid forced evaporative cooling, which is an important technique for cooling trapped atoms. We present the results of simulations for forced evaporative cooling in one, two and three dimensions.

We consider the peculiarities of the long-time evolution of the quantum wavepackets prepared in the range of the weakly anharmonic spectrum. We establish the revival periods connected with the contribution of the higher-order anharmonic corrections to the energy spectrum.

We consider the possibility of treating (e, 2e) experiments in the region of autoionizing resonances as `perfect experiments' in which parameters relating to the direct and resonance ionization amplitudes can be determined. An angle-independent parameter is defined for the autoionization of a doubly excited s-state to the s-state of an ion. Experimental values of this parameter from recent data for decay of the ( state of helium to the state of the helium ion are discussed. The more general situation involving states with L>0 is outlined.

Parametric four-wave mixing in Kr is described. When the 5p levels of Kr were excited by two-photon absorption of pulsed UV laser radiation, near-infrared radiation corresponding to , as well as a resonance line at 123.6 nm, were observed. It was demonstrated that both near-infrared and vacuum ultraviolet emission were highly directional. Polarization properties of near-infrared radiation are presented.

Judd proposed a delta-function model for f-shell correlation crystal field effects that uses an operator that is a product of two delta functions. This operator contains no parts that transform according to the irreducible representations [220] and [111] of the group . We explain these absences in terms of the ratios of certain factors. The corresponding operator for the d-shell is also discussed.

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Numerical calculations of the positions and widths for anticrossings in Rydberg Stark states are scarce, largely due to the results' sensitive dependence on the wavefunctions chosen. With wavefunctions derived from a kind of potential model as a basis, we calculate the positions and sizes for the anticrossings of potassium Rydberg states in a static electric field by means of diagonalization, and show that the results are in good agreement with available experimental data. The results show that this potential model can be used to deal with the problem of anticrossings, and the accuracy of the potential model is sensitively and numerically tested in the situation of external fields for the first time.

Odd-parity energy levels of the neutral europium atom (Eu I) have been investigated by employing both single-colour and two-colour stepwise laser excitation using the technique of resonance ionization spectroscopy in a heat-pipe thermionic diode system. Fifty-two new odd-parity energy levels of Eu I have been found in the energy region 40 575 - 43 410 . The J values for most of these new energy levels have been assigned unambiguously. In addition to this, 19 odd levels which were reported earlier, in the region of our present study, have also been investigated; the assignments of J values to nine of these levels have been confirmed and four levels, which had no unique J assignments, have been assigned definite J values.

We have implemented an integrable method with B-spline basis which allows us to calculate photodetachment cross sections of the ion in the presence of a constant electric field. The behaviour of the Feshbach resonances lying below the N = 2 and N = 3 thresholds is analysed in detail. Further insight on the relative importance of autoionization and tunnelling is provided by using a stabilization procedure. Our results permit us to explain most of the experimental findings and show the existence of resonance structures previously unobserved.

Photoion-yield spectra for Nd, Eu, Gd and Dy have been calculated taking into account the cascade of Auger and shake-off processes following photoionization of 4d, 4f, 5s and 5p shells. Global characteristics of Auger spectra as well as of transition zones are used to describe transitions between complex configurations. For all investigated elements a qualitative agreement with experimental spectra is obtained. The predominance of ions is mainly caused by the Auger decay of vacancy and shake-off processes. The production of abundant ions is determined by the selective population of low states for which the Auger decay is forbidden energetically. In Gd the significant part of such states become autoionizing states and it results in the majority of ions. The dominating signal is explained by the effective population of states with a vacancy through the direct photoionization and Auger decay of the excited configuration.

We present photoelectron spectra measured by `short' pulse ( ps) MPI of xenon at 526.5 nm excitation wavelength in the intensity range to . Ionization into and channels is observed and resonance structures are found in both ionization channels. They are induced by the AC Stark shift of bound Xe states within the light pulse which brings them into transient n-photon resonance with the Xe ground state. The resonant states are tentatively identified as d- and s-angular momentum states having AC Stark shifts which differ from the shift of the xenon ionization threshold. In the high-intensity limit, ionization into the channel is completely suppressed.

A Doppler-free kinetic energy release spectrum of has been recorded using a coincident time-of-flight technique, resolving vibrational structure in the optically active A , D and D electronic states. A comparison is made with earlier photofragment and optical measurements. The v = 7 - 10 levels of the A state, dissociating into the lowest atomic level , are observed in the spectrum. The lifetime of the v = 7 level was determined to ns while the absence of lower levels indicates lifetimes above . The D state was found to support only two vibrational levels, dissociating into . The observed levels of the A and D states may dissociate either via tunnelling through the potential barriers separating the levels from the dissociation continuum or via electronic predissociation. Experimental data of the D state indicate that optical transitions into the state dominate the decay of the v = 0 level, while electronic predissociation dominates the decay of higher levels. For the v = 0 and 1 levels of the D state predissociation is observed into the and the ionic states, while predissociation into the states is observed for the v = 2 and 3 levels.

Ionization and fragmentation processes of the NO molecule following the excitation of the nitrogen 1s electron have been studied by means of high-resolution mass-selective ion-yield measurements. The yields of and ions acquired with a quadrupole mass spectrometer (QMS) and a linear time-of-flight spectrometer (TOF) show surprising differences at the threshold region suggesting the selective attachment of the excited core electron to the centre during the dissociation of the ion. The fragmentation branching ratios corrected for the angular and kinetic energy effects are presented. The kinetic energy distributions of the and fragments have been extracted for a number of Rydberg states manifesting a significant dependence on l quantum number and energy of the primary excited Rydberg level. The lifetime of the core-excited state has been found from the shape of the low kinetic energy electron spectra acquired above the and thresholds.

State-selective measurements for single electron capture in collisions have been performed at 10 keV impact energy by means of translational energy spectroscopy and optical pumping of Na atoms with linearly polarized laser light for preparation of aligned Na(3p) target states.

Two methods have been used in the calculation of the integral excitation cross sections (ICSs) for the first time for the lowest five dipole-allowed transitions in e - scattering in the energy range from 200 to 1000 eV. The first method uses the universal extrapolation function together with the differential cross sections (DCSs) data, while the other uses Lassettre's equation and the Bethe theory. Good agreement has been obtained between the two methods at 500 eV. The calculation demonstrates that a significant contribution to the ICS comes from small scattering angles () where the experimental data are not available. Therefore a good extrapolation function is necessary in the calculation of the ICS from the DCS measurement in order to avoid the large uncertainties in the region of small scattering angles.

Ab initio calculations are performed on the scattering system, at low impact energies, using the R-matrix technique. The ground state and the lowest seven valence excited states, , and , of are included in the close coupling expansion with each state being represented by a configuration interaction wavefunction in a hybrid orbital set. Various approximations for the representation of the correlation between the target and the incident electron are investigated. Integrated and differential scattering cross sections are presented, and compared to experiment, for excitation from the ground level to optically forbidden levels. The results compare favourably with recent experiments in this energy region and remove a number of problems with our previous work.

Measured differential cross sections (DCSs) for electron-impact excitation of bending vibrational modes involving an odd number of vibrational quanta in by 4 eV incident energy electrons display a strong trend to zero for forward and backward scattering which is characteristic of `symmetry-forbidden' transitions. This DCS behaviour is postulated here to be produced by a Feshbach resonant mechanism involving a low-lying bent excited state of . The model described here identifies three additional low-lying bent excited states of which could also be parent states for core-excited Feshbach resonances, one of which may play a role in dissociative attachment in this 3.5 - 5.0 eV energy region. The resonant vibrational excitation mechanism proposed here is also believed to be operative in other polyatomic molecules and could be investigated by performing selected electron energy-loss measurements within the lowest energy resonance regions of the molecules and .

The third-order polarizabilities of substituted fullerenes are calculated by using the Su - Schrieffer - Heeger (SSH) model and the sum-over-states (SOS) approach. Numerical results show that there are larger static polarizabilities and resonant peaks in than those in X. For , the highest peak value of (at eV) is found to be about two orders larger than that for B, which may be important for its practical use.

Varró and Ehlotzky (1995) have employed an effective laser-induced polarizability to explain the breakdown of the Kroll - Watson approximation observed for small-angle electron - helium scattering in a laser field. Their derivation omits a cancelling electronic contribution so that the coherent polarization potential they introduce is much too weak to explain the breakdown.

In this recent review, the printers inadvertently printed figure 10 twice. The correct figure 11 is shown below.

Figure 11. The hydrogen and helium⁺ Lamb shift, the experimental value in (a) is from [2], in (b) from [16] and [15], in (c) from [42].

The correct version of equation (26) is:

Finally, the first sentence of the appendix should read: `In this appendix we briefly describe the calculation of the most difficult class of two-loop binding contributions that was performed by one of us (KP) [25], and consists of the diagrams shown in figure 8.'