Table of contents

Wendin's (1973, 1974) prediction of a collective resonance in the 5p spectrum of Ba I is explored for the lanthanide sequence. It is shown that a resonance does occur, and reasons why it is damped in La I and Ba I are advanced. The relevance of the conclusions to double photoionisation in Ba I and Eu I is explored.

It is suggested that energy coincidences between single- and double-ionisation thresholds for certain elements favour double ionisation by direct interaction between the incident photon and two electrons. The two-step autoionisation process which occurs in Ba I is shown to be less important for the elements considered.

Measurements are reported of the ratio of the ion count rates obtained in two-photon ionization of caesium atoms for linearly and circularly polarized light at the nine wavelengths of the argon-ion laser (514.5-454.5 nm). Comparison of this data with the recent theoretical values of Teague et al. (1976) and Flank et al. (1976) shows discrepancies at all photon energies except near the 7P resonance. In addition, upper limits are presented for the absolute two-photon rates in the rhodamine-6G wavelength region (563-635 nm).

The author has calculated the collision strength for electron-impact-induced transitions between the two fine-structure levels of the ground state of singly ionized carbon. At low incident electron energy the collision strengths are shown to be temperature independent by means of a calculation in which the total angular momentum is conserved. This fact is then used for making a close-coupling calculation which includes all the important terms.

The angular distribution of electrons ejected from the doublet resonant states 2p⁵(²P₁2,3/2/)3s² of sodium, calculated ab initio, is compared with two sets of experimental data for a number of angles and incident electron energies.

For pt.I see ibid., vol.9, p/L403 (1976). In part I the authors incorrectly stated the asymptotic conditions on the wavefunctions of the classical trajectory theory and also erred in describing the consequences of time-reversal invariance of the choice of integration constants (and limits of integration) associated with the phases of these wavefunctions. These errors are corrected and it is shown that there are many phase factors which yield integral and differential cross sections that are identical with those calculated on the basis of the Bates and McCarroll (1958, 1962) 'travelling-wave phase factors'.

The general electric multipole moment integrals are evaluated analytically, with an arbitrary origin of the electric multipole moment operator. The final results are expressed in terms of both the overlap integrals and the usual A and B functions.

Electron transmission experiments have been carried out in molecular nitrogen in the energy range between 1-4 eV, and values for the total cross section function for nine vibrational peaks in the ² Pi _g N₂ states in this region are tabulated.

When light propagates through a transparent medium, both the orbital and spin angular momenta of the light may change. It is shown by explicit calculation that the change in the angular momentum of the light is exactly equal and opposite to the change in the internal angular momentum of the atoms in the transparent medium. The centre-of-mass motion of the atoms does not play any significant role in this interchange of angular momentum.

In the configuration-interaction method for atoms, the Schrodinger equation is reduced to an infinite system of linear homogeneous equations. One then argues that the energy eigenvalues and eigenfunctions obtained by truncation from this infinite set of linear equations will converge, in the limit, to those of the original system. A proof is given which shows that this is essentially true for two-electron atoms and the configuration-interaction method does in fact lead to a convergent procedure. In the three- or more-electron case, it is shown that the linear operator which the infinite system of equations defines is not of the Hilbert-Schmidt type.

In a calculation of the energy eigenvalues and eigenfunctions of two-electron atoms, the authors have attempted to take into account most of the contributions from the repulsive term 1/r₁₂ by use of the formula theta (r₁-r₂)/r₁+ theta (r₂-r₁)/r₂= alpha /r₁+ alpha /r₂+(1- alpha )( theta (r₁-r₂)r₁+ theta (r₂-r₁)/r₂)- alpha ( theta (r₁-r₂)/r₂+ theta (r₂-r₁)/r₁) where alpha is a screening constant to be suitably chosen and theta (r) is the step function. Taking alpha =⁵/₁₆, the value at which the first-order perturbation energy for the ground state of helium vanishes, the authors have computed the energy eigenvalues and eigenfunctions of the first eight ¹S states of helium. The results are about as good as those obtained by Hartree-Fock methods.

The convergence patterns of the l expansion of the wavefunction for the excited 2¹S and 3¹S states of the helium atom are studied by means of the variational method. Particular attention is devoted to the radial energy limits.

Theoretical results based on the multiconfiguration Hartree-Fock approximation are reported for 4s²S-4p²P transitions of the Cu sequence. A partially extended Hartree-Fock model was used in which at last 3d orbital was not constrained to be the same as the rest. Some core-polarization effects were also included. Non-relativistic and approximate relativistic f values are reported and compared with observation.

Reports the classification of 220 spectral lines of Ti XIX, V XX, Cr XXI, Mn XXII, Fe XXIII, Co XXIV, Ni XXC, Cu XXVI, Zn XXVII, Ge XXIX and Se XXXI. The transitions identified are 1s²2p²-1s²2p3s, 1s²2p²-1s²2p3d, 1s²2s2p-1s²2s3s, 1s²2s2p-1s²2s3d, 1s²2s2p-1s²2p3p and 1s²2s²-1s²2s3p. These lines were emitted from laser-produced plasmas. Perturbation theory was used to calculate the wavelengths.

The lifetimes of nine levels of Ne I belonging to the 2p⁵4d, 2p⁵5d, 2p⁵4p and 2p⁵5s configurations have been measured by the delayed coincidence method. Seven of them have not been measured previously. The results are compared with calculations that have been assuming a pure j₁K coupling and the Coulomb approximation, and with intermediate-coupling calculations made by Gruzdev and Loginov (1973).

The cross sections for the excitation transfer between H and D atoms deduced from two previous publications are compared to those given by Kohmoto and Watanabe (1976). They are found to be in good agreement. The evidence for other effects such as the modification of the broadening and shift of the lines which are characteristic of these quasi-resonant processes is also emphasized and discussed.

Analyses the elastic scattering of electrons by the 2s state of atomic hydrogen at intermediate and high energies. For small and intermediate momentum transfers the eikonal-Born series (EBS) method gives reliable values of the scattering amplitude through order k^-2; the corresponding differential cross sections are much larger than for elastic scattering from the ground state. For large momentum transfers it is found that perturbation theory converges very slowly at intermediate energies (100 eV<or approximately=E<or approximately=500 eV) so that an exact (partial-wave) treatment of the static potential is more adequate. A corrected static approximation is found to reproduce the small-angle results of the EBS method and the large-angle static values.

High energy-resolution spectra of electrons scattered elastically from helium, neon and argon atoms have been obtained as functions of scattering angle and of incident electron energy. In addition to the well known levels of the lowest configurations of the temporary negative ions (resonances), the authors observe structures at energies close to those of the (core)np⁵(n+1)s levels of neon and argon. These structures are attributed to resonances having configurations (core)np⁵((n+1)s(n+1)p³P). By calibration against features occurring at known energies in the elastic scattering spectra and also metastable excitation spectra they determine accurately the energies of the observed resonances.

The X-ray production cross sections and yield ratios for the L lines and the total L shell, measured by electron impact ionization in the bombarding electron energy region 300-600 keV, are determined for Yb, Au and Pb. The experimental data are compared with theoretical calculations.

The authors discuss a new type of emission, in which the electronic transitions are induced by the movement of the nuclear charges. The vector potential A=A^cl+A^q consists of the classical field of the nuclei A^cl and the radiation field A^q. In a non-relativistic treatment the transition is due to the operator (e²/mc²)A^clA^q instead of (e/m)pA^q. The induced radiation is anisotropic. It is relevant if (e/c)A^cl is comparable with the electronic momentum p. This is the case for outer-shell (M,N) transitions in a system of rapidly moving heavy nuclei. This effect can therefore produce a considerable part of the observed anisotropy in the quasimolecular outer-shell spectra. For inner-shell (K,L) transitions, however, the induced radiation is too small to explain the large measured anisotropy.

Two distinct X-ray continuaC1 and C2 above the characteristic lines are observed in high-energy collisions between atoms with atomic numbers of 28 to 57. This structure is explained by a superposition of K molecular-orbital (KMO) radiation and of an intermediate L-K molecular-orbital (ILKMO) radiation of high intensity which is due to 2p sigma vacancies. In the framework of the dynamical theory of intermediate molecular phenomena and using a scaling of the H₂⁺ correlation diagram with screened state-dependent charges good agreement between the shapes of the measured and calculated spectra is obtained.

Non-adiabatic matrix elements H_cj(k,R), Q_cj(k,R), V_cj(k,R) and D_cj(k,R) connecting the states of the discrete j=(1s sigma _g,2p sigma _u) and continuous c=(klm) spectra of the two-centre problem with quantum numbers l=0(1)7 and m=0 are calculated in the range k=0.1(0.1)1(1)10, R=0.1(0.1)20 with an absolute accuracy of approximately 10^-5.

Absolute experimental cross sections are presented for elastic differential scattering of electrons by molecular hydrogen at impact energies between 100 and 2000 eV and at scattering angles between 5 and 50 degrees . The results are compared with the relative experimental cross sections of previous experiments and with the data of different theoretical calculations. Total elastic cross sections are considered as well. The present absolute molecular hydrogen cross sections, together with the 100 and 200 eV ratio measurements of the differential elastic cross sections of H₂ and H of Lloyd et al. (1974) were used to obtain a new set of absolute elastic cross sections for atomic hydrogen. These experimental data are compared with the absolute experimental sections obtained by Williams (1975) and with theory.

Vibrational excitation in H⁺-CO₂ collisions has been measured with the crossed-beam method in the energy range E_Lab=15-50 eV and for scattering angles delta _Lab=0-12 degrees which include the rainbow region. With an energy resolution of about Delta E=50 meV, excitation of the various modes of CO₂ can be clearly resolved. A pronounced selectivity is found for vibrational excitation, depending on energy and angle. For scattering angles near zero the dominant transition is 010 excitation, whereas the rainbow region at higher energies shows a strong inelasticity with dominant excitation of the asymmetric stretch mode. Small-angle scattering is interpreted by a simple model, the Born approximation with long-range electrostatic interactions.

Results are presented for the experimentally determined transition probabilities for the Ar I line at 430 nm and the Ar II line at 480.6 nm using both pure argon diagnostics and H beta electron density diagnostics applied to a wall-stabilised arbon arc LTE plasma. Full profile fitting of H beta at N_c approximately=2*10²³ m^-3 using the Stark-broadening data of Griem (1974) yields electron densities approximately 11% lower than the data of Vidal et al. (1973), the latter being within 2% of the pure argon diagnostic value. Using the pure argon diagnostics, the transition probabilities are: Ar I at 430 nm, A_ki=0.372*10⁶ s^-1; Ar II at 480.6 nm, A_ki=74.9*10⁶ s^-1. Continuum emission coefficients are also given at 431.4 and 482.7 nm.

For pt.II see ibid., vol.7, p.L359 (1974). Examines the effects of an external homogeneous electric field on the process of resonant ionisation of atoms interacting with a metal surface. These effects considerably reduce the probability of electron tunnelling into the metal when the electric field is directed towards the surface. The process of field ionisation of the atom is also considered. The atom-metal interaction enhances the probability of field ionisation.