Table of contents

Following Schuda et al. (1974) the effect of the adjacent F=2 to F=2 transition on the fluorescence spectrum of the F=2 to F=3 transition in the sodium D₂ line is studied. The spectrum is essentially three-peaked. A small asymmetry is predicted; but inclusion of such a lower level is found to enhance the low-frequency side of the spectrum rather than the high-frequency side as was observed experimentally.

The singlet-triplet anticrossing method has been employed to measure the n¹D-n³D intervals in helium for n=8 to 11. The results, in MHz, of 9326+or-35 (n=8), 6644+or-35 (n=9), 4889+or-30 (n=10) and 3696+or-30 (n=11) support recent improved theoretical calculations by Chang and Poe (1974).

Light shifts of the ground state HFS transition in a ¹³³Cs vapour, produced by a CW narrow-band tunable GaAs laser matched to the D₂ resonance line have been investigated. The 0-0 transition microwave frequency was accurately measured as a function of the laser frequency. For usual optical-pumping light intensities, excellent agreement is found with theory. At higher intensities, distortions appeared in the resonance curves. A new frequency-stabilization method of lasers is suggested.

The parity-violating E₁ transition matrix elements between the 6s and 7s states of atomic Cs to be expected on the basis of the Weinberg-Salam model of neutral weak currents has been calculated. It is found that iE₁^6s,7s=3.60*10^-11 atomic units, in excellent agreement with a calculation by Bouchiat and Bouchiat (1975) using a different method.

Photoabsorption coefficients of krypton and xenon have been measured to +or-5% accuracy in the 48-210 AA region using a synchrotron radiation source and channel electron multiplier photodetection.

Kinetic secondary-electron emission from both surfaces, i.e. in the backward and forward directions, is measured and compared with a proton beam (20-250 keV) traverses thin carbon foils. It is found that total forward emission is larger than backward emission by a factor of up to 1.55. Electron energy distributions, measured using a retarding field suggest that an essential contribution to the production of secondary electrons, emitted with energies down to a few eV, originates from binary collisions of the protons with individual electrons in the target.

The recent theory of Cleff and Mehlhorn (1974) on the angular distribution of Auger electrons is applied to explain the angular distribution of electrons ejected by autoionization of the 2p¹¹D state of helium, as observed in He⁺-He collisions at 15 keV. The unequal populations of the ¹D magnetic sublevels are explained by a quasi-molecular excitation mechanism; the population of the sublevels mod M_L mod =1 and M_L=0 is ascribed to a rotational coupling at large internuclear distance.

Chlorine beam L X-rays were detected using a curved crystal spectrometer. Special attention is given to the observed 2p⁵ to 2p⁴3s multiplet transitions. The L X-ray line intensities for these multiplets in chlorine do not support statistical population of the initial states, in contrast to previously reported chlorine data.

Using the generalized valence bond model (GVB), potential energy curves for the ^1,3 Sigma , ^1,3 Pi , ^1,3 Delta states of ScH are presented. All states are bonding with at most a weak barrier and the ³ Delta is the lowest energy state. The bonding is primarily to the 4s² state of Sc. These results are contrasted to like studies of H on Fe, Ni, Mn and Cu. The implications of this study to hydrocarbon catalysis by first-row transition metal catalysts are explored.

Published measurements on the D(¹ Pi )-x ¹ Sigma ⁺ bands of gaseous ⁶⁵Cu³⁵Cl are reanalysed. The new value of the Lambda -doubling constant, q, for the D(¹ Pi ) state is approximately equal to the value expected for the case of pure precession of a p electron, assuming E(¹ Sigma ⁺) to be the state mainly responsible for the doubling.

The calculations of Drake and Holt (1975) for the collinear collision of He+H₂ have been repeated using more accurate H₂ vibrational wavefunctions. The transition probabilities are reduced by approximately 10%, showing the sensitivity of this process to the intramolecular potential employed. Transition probabilities for an equivalent Morse potential are also presented.

Interelectronic angular distribution functions p( theta ₁₂) and 'angular holes' have been examined for correlated descriptions of several excited states of He. One- and two-particle expectation values were determined, including tau -an overall angular correlation coefficient. Although significant differences were observed between the p( theta ₁₂) curves for the singlet and triplet multiplicities of the 2P state, the 'angular holes' were, in all instances, of similar shape to that obtained for the ground state: however, by comparison, the depths of the excited state 'holes' at theta ₁₂=0 were all considerably reduced in value. The detailed structure of the curves enabled observations to be made regarding variations in the electronic shielding of the nucleus and, in particular, allowed a restatement of Hund's multiplicity rule to be substantiated.

Spin-projected Hartree-Fock calculations using general spin orbitals are performed on some S, P, D and F states of Li and on the ground states of its isoelectric ions with Z=4-10. The energy -7.447596 au is obtained for Li 2²S, compared to -7.447565 au with the spin-optimized SCF method and -7.432727 au with the ordinary restricted Hartree-Fock method. Full configuration-interaction results for the same basis sets are also reported.

The R-matrix theory of electron-atom scattering using the Dirac Hamiltonian is formulated in a similar way to that used in the non-relativistic case. The expression for the R-matrix in terms of the surface amplitudes is exactly the same, but the boundary condition at r=a for the continuum orbitals is modified. The matching process at the boundary gives the K matrix, from which the S matrix and cross sections can be derived. A general computer program implementing this procedure is now being written.

It is shown that for S-S atomic transitions the Schwinger variational principle with sufficiently flexible one-state functions does not take account of long-range polarization effects, even though the Schwinger formalism explicitly contains long-range terms. The plane-wave (1,1) Pade approximant to an S to S transition in general exhibits long-range behaviour. However since this approximant is obtained by applying the Schwinger principle to rather restricted one-state trial functions its accuracy must be called into question.

The 90 degrees optical polarization of Lyman alpha and the Fano-Macek (1973) orientation and alignment parameters of the 2p state of H have been calculated in the Coulomb-projected Born approximation and its generalization. Results are presented for the polarization resulting from impact with electrons with energy in the range 40-200 eV. Contour maps for the rate of coincidence between scattered electrons and Lyman alpha photons emitted in the scattering plane are given for incident energies of 100 eV.

The off-shell exchange matrix element of the operator Y_{beta alpha} ⁽¹⁾ for the electron-hydrogen scattering problem has been evaluated analytically. This matrix element is required when one is interested in applying the form of the Lovelace-Faddeev equations due to Sloan and Moore (1968) to atomic scattering problems.

The lowest two of the previously reported e⁺-H S-wave resonances just below the n=2 hydrogen excitation threshold are studied using the stabilization method. They are found to be artifacts of the close-coupling approximation and to disappear if the correlation effect is taken into account. The so-called anomaly-free variational methods are not free from these spurious resonances if the trial function corresponds to the 1s-2s-2p close-coupling approximation or to other approximations very similar to it.

Experimental absolute differential cross sections (DCS) for the excitations 1¹S to 2¹P and 2³P in helium are reported at incident electron energies of 60 eV and 80 eV, and at scattering angles between 5 degrees and 136 degrees . By combining the present DCS measurements for the 2¹P excitation with results of recent electron-photon coincidence measurements, absolute DCS for the excitation of the individual magnetic sublevels 2¹P₀ and 2¹P_+or-1 are obtained from purely experimental data. These magnetic sublevel cross sections, as well as their sum, are compared with results of calculations in the multichannel eikonal, distorted-wave and first-order many-body theories.

The distorted wave polarized orbital approximation is applied to the excitation of 4¹S and 5¹S levels of helium. Results are presented for total cross sections over an electron impact energy range of 25 to 400 eV and also for small-angle differential cross sections at impact energies of 50, 60, 100 and 200 eV. These are compared with experiment and the accurate Born results of Bell et al. (1969). The introduction of explicit s-p coupling into the T matrix has a marked influence on the small-angle differential cross sections, producing a strong enhancement, and bringing them into close agreement with experiment at the highest energy considered.

An integral form of the close-coupling approximation by Ghosh and Basu (1973) and Chaudhuri at al. (1974) has been employed to investigate the processes e⁺+He(1s²) to e⁺+He(2s²) and e⁺+He(1s²) to (e⁺e^-)+He(1s). Couplings of the excited states of both the helium and positronium atoms have been neglected. Results obtained by using an approximate form of the close-coupling approximation which neglects some strong distortion effects are presented. The results in two-state close-coupling approximation do not show good agreement with the experimental findings below the positronium formation threshold. The effect of exchange of electrons is found to be appreciable in the low-energy region.

The mobilities of Li⁺, Na⁺ and K⁺ ions in He gas have been measured at gas temperature 38, 36 and 37 degrees C respectively. The obtained zero-field reduced mobilities 23.2, 22.8, and 21.4 cm² V^-1 s^-1 for Li⁺, Na⁺ and K⁺ ions, respectively are similar to those reported before.

For pt.I see ibid., vol.7, p.1543 (1974). Quantal close-coupling calculations of Na(3²P_jmj)-He(¹S) collisions are presented. The Baylis (1969) and a combined Baylis-Krauss et al. (1971) potentials are investigated in the temperature range 400K-4500K. The cross sections for population transfer, multipole relaxation and coherence transfer appropriate to gas-phase experiments, and the population transfer cross sections for beam experiments, are opacity analysed and the opacity functions are studied as a function of l. The ranges of l contributing to depolarization and inelastic processes overlap and cross sections are of similar magnitude. Rotation of the internuclear axis is the main transition mechanism and the cross sections can be characterized by the three Grawert parameters.

For pt.II see ibid., vol.8, no.14, p.2393 (1975). Fully quantal calculations of the width and shift of the Na D double due to collision with He(¹S) in the temperature range 400K<or=T<or=3500K are presented. This is the first time that Baranger's fully quantal impact theory (1962) has been applied to the broadening of spectral lines by neutral perturbers. The complex cross section is opacity analysed and the complex opacity functions are studied as a function of l. The statistical approximation can be used at low l and can reproduce the total width with the cut-off impact parameter decreasing with increasing temperature. Inelastic processes contribute significantly to the width. The shift is an order of magnitude smaller than the width.

Absolute X-ray spectroscopic measurements of the lines and continua from space-resolved C⁶⁺, C⁵⁺, C⁴⁺, C³⁺ ions at the surface of a plane polyethylene target, irradiated by a 1.06 mu m neodymium laser, are interpreted in terms of a collisional-radiative model in which some of the allowed lines are optically thick. The degree of ionization increases monotonically with laser power density over the range 10¹¹ to 2*10¹² W cm^-2 and the electron energy distributions are strictly Maxwellian. The ion population ratios indicate that the ionization time is of the order of 1 to 10 picoseconds and is limited by thermal expansion within a thin layer whose mean density is approximately 3*10²¹ cm^-3.