Table of contents

Neon K X-ray spectra resulting from O⁴⁺ and Cl⁴⁺ bombardment are observed to have dissimilar K alpha satellite intensities. These results are in contrast to similar measurements made using C⁶⁺, N⁶⁺ and O⁶⁺ bombardment.

110 MeV sulphur ions with initial charge 11⁺ and 15⁺ are passed through thin copper foils. Yield ratios between Cu-K and projectile REC X-rays elucidate mechanisms for the production of target X-rays in fast heavy ion collisions.

The cross sections for electron loss from and destruction of fast metastable helium ions. He⁺(2s) passing through ground state atomic hydrogen are calculated using the first Born approximation. The theoretical predictions are in reasonable agreement with measurements of Gilbody and Shah (1974).

Preliminary differential scattering results are reported on charge exchange into the ²P_1/2 and ²P_3/2 fine structure levels of Xe⁺ in H⁺ and D⁺ collisions with Xe in the laboratory energy range from 120 to 712 eV. Time of flight techniques used for state identification show the dominance of the ²P_1/2 level at low energy. Cross sections are determined and the results interpreted in a molecular framework.

The effect of the hydrogen bond interaction on the Compton profile for water is estimated by observing the consistent trend in the water polymer (monomer, dimer, trimer, tetramer and pentamer) profiles obtained from various quality wavefunctions. The profile of the isolated water molecule is found to be lowered by hydrogen bonding.

On the particular case of a two-level atom perturbed by a quasi-resonant radiation, it is shown that the use of tunable CW dye lasers should allow the observation, in the optical range, of some nonlinear effects (resonance shift, multiphoton resonances) for rather low light intensities (a few Wcm^-2). The theoretical treatment which has been chosen is based on the formalism of the dressed atom and it takes into account spontaneous emission in a phenomenological way.

Details are given of a multi-channel asymptotic method for the calculation of the free-free transitions of negative ions; the method is illustrated with an application to the negative lithium ion.

For pt. IV see abstr. A.47877 of 1974. The triple differential cross section for the electron impact ionization of helium is calculated in the Coulomb projected Born approximation, including exchange. Detailed comparison is made with the ordinary Born result and with available experiment in both the coplanar and non-coplanar geometries. The agreement with experiment in almost all cases is appreciably better for the Coulomb-projected Born results than for the ordinary Born results.

Absolute apparent cross sections for electron-impact excitation of helium to the 4³D level measured as a function of target-cross pressure (3*10^-5<p<3*10^-3 Torr) have been analysed by means of the 'F-cascade model'. proposed by St John and Fowler, (1961), in order to study the process of collisional transfer in helium. Special attention is paid to imprisonment of resonance radiation. It is found that scaling of the collisional transfer cross sections with a power of the principal quantum number n leads to results which are inconsistent with the experimental findings. By extrapolation of the apparent 4³D cross section to zero pressure we are able to estimate electron-impact excitation cross sections for the 4¹F level.

Spectroscopic constants for NF are determined from a Dunham analysis of potential energy curves computed previously by means of a valence configuration interaction method. Results are presented for several experimentally known and unknown states within the ³ Sigma ^-, ¹ Delta , ¹ Sigma ⁺, ¹ Sigma ^-, ³ Delta and ³ Sigma ⁺ symmetry species. Where possible, our findings are compared with other calculations and with experiment.

Theoretical results are presented for the photodissociation cross section of H₂⁺ from the 1s sigma _g ground electronic state to the vibrational continuum of the 2p sigma _u state. Values of the cross section have been calculated for rotational states 0<or=J<or=8. A total cross section has been evaluated for temperatures 2500<T(K)<26000, in the wavelength region 500<or= lambda (AA)<or=25000, assuming a Boltzmann distribution. The variation of the cross section with temperature is discussed. It is concluded that for T>or=10000K, the total cross section would be improved by including more rotational states. An empirical extrapolation procedure is proposed using the available results to obtain cross sections accurate at high temperatures.

For pt. III see ibid., vol.5, 2098-106 (1972). State selected rotationally inelastic collision processes have been studied in Na₂(B¹ pi _u) using laser induced fluorescence. As an extension of earlier measurements, the authors investigated levels with very high rotational quantum numbers: (v,J)=(0.152),(5,124) and (14,118). Collision partners are all rare gases. Asymmetries sigma ( delta J=+1)/ sigma ( delta J=-1) as large as 4.6 are found, evidence for very efficient dissociative collisions is reported and the temperature dependence of the asymmetry is shown for some levels with J<100 and Ne, Ar and Kr as collision partners.

The elastic, momentum transfer and rotational excitation cross sections for low energy positrons scattered by hydrogen molecules are calculated using respectively, spherical and spheroidal coordinates and harmonic expansions. Both the spherical and the spheroidal calculations are done in the adiabatic-nuclei approximation. The harmonic expansions in the two coordinate systems are both truncated at corresponding order (up to and including d-waves). The calculations are identical, save for the fact that partial spherical analysis is used in one case and partial spheroidal analysis in the other. The two sets of results so obtained turn out to be almost identical.

A method for calculating charge exchange cross sections is generalized to provide a description of p+H₂ charge transfer processes. The assumptions and the conditions for the validity of the method are discussed. The results are compared with experiments on total charge transfer, capture into the 2S state of hydrogen and H₂ are considered. Comparison with experiments and the predictions of Tuan and Gerjuoy is carried out.

The decay of H₂ molecules produced by charge transfer reactions in H₂⁺+H₂ collisions is investigated. Dissociation processes are observed to be important in explaining the experimentally observed total cross section for charge transfer. Experiments on the highly excited states of hydrogen molecules produced in the above charge transfer collisions are analysed and compared with theoretical arguments on the decay of Rydberg states of molecules. Vibrational autoionization is shown to be an important factor in the interpretation of these experiments.

The Lyman spectrum of carbon VI from the expansion plume of a laser-produced plasma has been interpreted to give the absolute distribution of electrons amongst bound and free energy states. Local thermal equilibrium is shown to be attained for bound states equal to and above a certain principal quantum number. Plasma densities and temperatures have been deduced from spectral intensities at distances of 1.0-2.8 mm from the target. Spectral intensities have also been interpreted in conjunction with plasma parameters and certain theoretical de-excitation rate coefficients to give the (collisional-radiative) recombination coefficient for the recombination of C⁶⁺ to the hydrogen-like C⁵⁺, and this is compared with theory. The coefficient for purely two-body recombination to the ground state of C⁵⁺ has been deduced from the free-bound continuum intensity.

A radiative cascade model is used to calculate the excited state population densities of a recombining oxygen plasma. The model is expected to be valid for the low quantum number S, P, and D levels for electron densities below 10⁶ cm³. The radiative recombination coefficients for the S, P, and D series and the Einstein A coefficients for transitions between members of these series are calculated by the quantum defect method. All levels with l>or=3 are taken to be hydrogenic. The excited state densities are found for the two limiting cases in which the transitions to the ground state are either optically thin or optically thick. The emission line intensities from cascading are calculated.