Table of contents

Spectra emitted from laser-produced plasmas of Ru and Rh have been recorded in the 250-500 A range. The authors have measured the wavelengths of 4s²4p²-4s4p³ transitions and have found excellent agreement with theoretical data and also with scaled multiconfigurational Dirac-Fock calculations.

The A¹ Sigma ⁺-X¹ Sigma ⁺ system of KRb was excited using a titanium-doped sapphire laser. Fluorescence spectra were recorded on a Bomem Fourier transform spectrometer, using an apodised linewidth of 0.045 cm^-1. Rotational and vibrational constants are reported for the ground state, X¹ Sigma ⁺, covering the range 0<or=v<or=44 and J<141.

The conditions under which chiral effects can be observed in elastic electron scattering from diatomic oriented molecules are discussed. It is emphasised that it is essential to separate helicity-flip and non-flip contributions to the various observables and that only the non-flip terms can be considered to be chirality dependent.

Spin effects for electron-impact excitation of Hg(6³P₁) have been studied for small scattering angles ( theta _e<or=30') and energies of 15, 30 and 50 eV. In an electron-photon coincidence experiment the linear polarisation components P₁ and P₄ (for photon emission angles perpendicular and parallel to the scattering plane, respectively) have been measured from which the relative spin-flip cross section rho ₀₀ could be determined. It has been found however, that reliable results are obtained only if various corrections, which have not been discussed in previous investigations, are taken into account. With these corrections the data agree well with predictions of widely accepted theoretical models. As an example, this is demonstrated by comparing the experimental data with a DWBA calculation. In particular rho ₀₀ is zero with the experimental accuracy for small scattering angles ( theta _e(10') at E=50 eV.

Single-centre partial-wave expansion and partial-wave decomposition of the overlap integral are obtained for Hermite Gaussian functions. The resulting formulae are completely analytical and particularly suitable for numerical implementation on a computer. The corresponding expressions for other systems of polynomial Gaussian functions (Cartesian, spherical, etc.) can be easily written in terms of the formulae presented.

The effect of non-transferable intershell correlation effects on the energies of the LS states determined by the 4f² electronic shell is studied for Pr³⁺ by means of a series of configuration interaction calculations defined in terms of configuration state functions (CSF). Some attention is paid to the problem of dealing with the large number of CSF corresponding to a single orbital configuration but characterised by various coupling schemes of the spin and orbital angular momenta. It turned out that the dominant internal, semi-internal and core polarisation effects are represented by configurations corresponding to the excitations 4d² to 4f², 4d² to 4f5f, and 5s to 5d, respectively. The latter configuration has the strongest effect on the LS term energy differences.

In this paper the authors describe a semi-empirical, approach for calculating certain high-order perturbation effects in a simple manner. They use these modified orbitals in RPA type equations to give values for E1 transition matrix elements and hyperfine dipole constants that agree well with experiment. Including the spin-independent weak interaction leads to parity non-conserving equations. For the caesium 6s₁2/ to 7s_1/2 parity non-conserving E1 transition they obtain 0.904(1+or-0.02)*10^-11 (-iea₀Qw/N).

The analysis of experimental data on negative ion yields in the interaction of electrons and molecules in organic compounds shows that there occurs an electronically excited Feshbach resonance involving singlet excitation of a molecule and capture of an additional electron into the fully symmetric Rydberg orbital produced by the singlet polarisation potential.

It is well known that the Sommerfeld screening parameters sigma ₁ and sigma ₂ for a spin doublet of levels can only be calculated if the individual energies of the two members of the doublet are known. In several cases, the resolution of the experimental method for finding the energies has proved insufficient and so only the energy of the unresolved doublet of levels has been reported. A new method has been developed for calculating these parameters for a spin doublet of levels by using the unresolved experimental energy values given by Bearden et al (1967). The results of the authors' calculations are presented. It is found that the energy values calculated by using these parameters in the Sommerfeld energy expression are in very good agreement with resolved experimental energy values of the individual components of different spin doublets.

Mass polarisation corrections are computed to the first order of perturbation, for the lowest M_L=0 to -2 bound states of H^- and He in a strong magnetic field (B>or=1 MT). The zero-order energies and wavefunctions are provided by a previous variational calculation. The mass polarisation corrections split into two components, respectively longitudinal and transverse to the field. Like the field-free mass polarisation, the longitudinal component remains weak for all the states studied. However, the -1^-_s, -1^-_T and -2⁺_s transverse mass polarisation corrections become significant with respect to the binding energy when the magnetic field is sufficiently high.

Low-pressure broadening and shift of three spectral lines of argon: 667.7 nm (3p⁵4s-3p⁵4p), 430.0 nm (3p⁵4s-3p⁵5p) and 360.6 nm (3p⁵4s-3p⁵6p), emitted from a low current glow discharge in pure argon, Ar-Ne and Ar-He mixtures have been investigated by means of a Fabry-Perot interferometer. The values of the pressure broadening and shift coefficients are determined.

Doubly excited neutral states of neon, 2s²2p⁴nln'l', have been investigated using photoelectron spectroscopy with synchrotron radiation. The selective decay of these levels into all the energetically accessible ionic states in the range 50-60 eV has been measured. In addition, decay of Ne⁺ states, with binding energies above the first double ionisation potential, by autoionisation to the Ne²⁺(³P) state has been observed.

The decay of doubly excited resonances of neutral xenon into all the accessible main line and satellite ionic states has been studied using photoelectron spectroscopy and synchrotron radiation between 20.5 and 26.2 eV. The results show that resonances dominate the satellite cross sections in this region and that they decay selectively into individual J levels of the ion.

A non-perturbative, complex eigenvalue, laser ionisation many-electron theory which incorporates the effects of the simultaneous presence of a DC field is presented. Application is made to the H^- ionisation cross section with AC fields up to 10¹¹ W cm^-2, with and without a DC field. The effect of the ground state correlation is of the order of 30%. Most important is the degree of accuracy of the representation of the Gamow function describing the free electron. The Gamow function is expanded in terms of a large number of spherical harmonics (up to l=16), each associated with a large number of complex-coordinate-scaled Slater orbitals. Convergence is tested thoroughly via the overall stability of the resulting complex eigenvalues.

The authors have measured the electron impact induced fluorescence spectrum of N₂ in the wavelength range 102 to 134 nm at a spectral resolution of 0.05 nm. The experiment was performed in a crossed beam configuration under optically thin conditions. Their spectral measurements provide the emission cross sections of the transitions of the b¹ Pi _u-X¹ Sigma ⁺_g Birge-Hopfield I-band system. The structure and vibrational population distribution of this system are strongly affected by a configuration interaction of the valence b¹ Pi _u and Rydberg c¹ Pi _u and o¹ Pi _u states. Analysis of electron energy loss data shows that there perturbations give rise to excitation cross sections whose upsilon ' dependence is strikingly different than the variation of the Franck-Condon factors of the unperturbed diabatic states.

The 3 mu m band of methyl fluoride which is a symmetric top molecule, has been studied as a function of pressure in the regime down to the Doppler limit. A range of rotational quantum states has been accessed so that variations with the angle between the axis of rotation and the axis of symmetry could be investigated. Results are discussed with reference to Anderson-based theories of pressure broadening, which are found to be inadequate. The data were obtained using a laser mixer 3 mu m source, which is also described.

A relativistic distorted wave model is formulated to describe the ionisation of K-shell electrons in a target atom produced by the impact of a bare ion at relativistic energies. The model introduces the continuum of the projectile in the entry and exit channels in order to satisfy the asymptotic Coulomb boundary conditions. Cross sections, differential in the angle of the ejected electron and in its energy, are calculated. They show a binary peak and the cusp of the capture to the continuum. Total cross sections are compared with experimental values.

Cross sections for the transfer of excitation between fine-structure sublevels of the 8D and 9D states of caesium due to collisions with noble-gas atoms are measured by the integrated intensities method. The results for the 9D state are in good agreement with the values obtained previously by the time-resolved technique and those for the 8D state are reported for the first time. The final values of the cross sections for the process Cs(n²D₃2/)+A to Cs(n²D₅2/)+A, summarising the authors present and previous measurements, are, for A=He, Ne, Ar, Kr and Xe, respectively, 7.9 (1.3), 2.8 (4), 1.9 (3), 1.4 (2) and 1.4 (2) for n=8, and 7.5 (1.2), 2.4 (4), 2.2 (4), 3.1 (5) and 3.1 (5) for n=9, in units of 10^-14 cm².

The authors have observed autoionisation of atomic fragments following dissociation of oxygen compounds (O₂, CO₂, N₂O, H₂O, SO₂) and CF₄ induced by negative-ion (O^-, F^-, H^-) and proton impact at energies of a few keV. The autoionising atoms were identified by the characteristics of the ejected electron spectra observed in electron spectroscopy.

A semi-phenomenological method to compute the cross section for bound shell ionisation of atoms by impact of relativistic electrons is proposed. This method involves a simple schematisation of the Bethe surface, which is obtained from the experimental optical oscillator strength distribution. The authors' approach may be used to describe the ionisation from any bound shell. They consider in detail the case of K-shell ionisation and derive an analytical formula for the differential cross section on the basis of a hydrogenic optical oscillator strength density. Close collisions are described by the Moller differential cross section, thus incorporating exchange effects. Empirical corrections to the Born approximation for energies near the ionisation threshold are introduced. The relationship of their approximation and the Weizsacker-Williams method of virtual quanta is also discussed.

A theoretical consideration of PCI in the processes of inner-atomic shell ionisation by fast electron impact is given. The shift of the maximum of the Auger line is calculated for a number of Auger transitions in the atoms of noble gases and lanthanum. The consideration is based on the eikonal theory.

Excitation of the 4p⁵(²P_3/2)5s³P₁ state of krypton by 30 eV incident electrons has been studied using the electron-photon angular correlation technique. The alignment and orientation of this state can be completely described using four independent parameters, three of which can in principle be obtained from the present measurements of angular correlations with two detector geometries. Difficulties encountered in the extraction of the spin-dependent parameters are discussed. There is generally good agreement between the experimentally measured angular correlations and distorted-wave Born approximation predictions.

An electron spectrometer employing differential pumping and a position-sensitive detector has been used to obtain high resolution electron energy-loss spectra of HBr and DBr between 8-16 eV. A wide range of scattering conditions have been employed resulting in the observation of electronic states and the assignment of a number of Rydberg series.

The flux of caesium ions desorbing from a hot Ir surface has been studied by electrostatic means at energies below 400 eV, and with detection in a well shielded Faraday collector. The caesium diffuses through the iridium metal foil at temperatures of 1300-1400 K. Two grids at variable voltages are used to analyse the flux. Signals up to 10^-4 A cm^-2 are measured under varying conditions. In the flux, positive ions are observed with positive emitter voltage, while negative ions are found with negative emitter voltage. The positive ions may change sign to negative ions in contact with surfaces with a large probability, and their transport is strongly influenced by the electric fields. The authors conclude that the positive ions are in excited states. The negative ions may eject electrons in contact with the collector surface and appear as positive ions, which shows that they are excited.

Isotope shifts and hyperfine structures of six excited levels between 17790 cm^-1 and 21346 cm^-1 in Nd I were measured by means of atomic-beam-laser spectroscopy. Anomalies caused by the second-order hyperfine perturbation between two close-lying levels were studied for ¹⁴³Nd and ¹⁴⁵Nd. It was found that the anomalous energy shifts were caused predominantly by the second-order dipole-dipole hyperfine perturbation and that the contributions of the dipole-quadrupole and the quadrupole-quadrupole perturbations were negligibly small.

It is shown that the 'electron shelving scheme' used in experiments on quantum jumps in single atoms may serve as an effective tool for investigation of electron dynamics in spatially distributed quantum systems. The statistics of long interruptions in resonance fluorescence of a single impurity incorporated into a model lattice system is considered. It is shown that the statistics reflects the character of the electron motion on the lattice in the vicinity of the impurity. Both the cases of coherent and incoherent electron dynamics are discussed.