Table of contents

Spin-orbit interaction results in radial matrix elements which depend on the j' state of the continuum wavefunctions. This is taken into account in evaluatingthe angular asymmetry parameter and its dependence on photon energy using experimental values of the spin-orbit perturbation function for caesium. The effect of circular polarized light to photoionize spin polarized atomic beams is also considered.

Absolute angular differential cross sections for the elastic scattering of electrons on argon atoms have been measured for incident electron energies of 40.002 and 50.128 eV over the angular range 20 to 150 degrees. An angular resolution of 0.02 radians has revealed two deep minima in the cross sections at about 67 and 140 degrees. The cross section values generally agree well in angular dependence, except for angles less than 30 degrees, with an exchange plus polarization approxi- mation calculation by Thompson and a relativistic calculation by Walker. However, both theoretical approximations yield cross section values which are about a factor of 1 a 3 higher than experimental values. All previous experimental measurements have not revealed the true depth of the cross section minima. The present measurements have been made with crossed electron, modulated atom beams. Cross section values have been made absolute by measuring elastic scattering cross section ratios for argon, atomic hydrogen and helium and using a phase shift analysis of the scattering around the 19.355 eV resonance in helium.

Absolute values of the angular differential cross sections for the elastic scattering of electrons from atomic hydrogen have been measured for incident electron energies of 3.4 eV and 8.7 eV and over the angular range of 30 to 150 degrees. The experimental method was bascd upon the standard crossed electron, modulated atom beam method with high resolution (0.07 eV) energy analysis of the incident and scattered electrons. The accuracy of the present measurements is 6 % which permits distinctions to be made between thevarious theoreticalapproximations. It is shownthat the variational calculated values and the pseudo-state close coupling approximation values (Burke et aZ1969) are in good agreement with measured values over the complete angular and energy range. The three-state close coupling and one-state static exchange approximation values agree with experimental values only at 8.7 eV for scattering angles greater than 90".

The absolute total cross section for excitation of the 2p state of atomic hydrogen by electrons is examined in detail in the first electron volt above the 2p threshold. Only a single resonant state ('P) is found just above the threshold. An absolutevalue of the total 2p excitation cross section of 0*276_',4b"I," xuo2 at 11.0 eV is determined by calibration of the apparatus relative to the differential elastic scattering cross section value of 0.727 xaoa sr-' at 60" and 8.70 eV and by calibration of the Lyman alpha detector. These experimental measurements do not require any corrections for cascade radiation and do not depend upon any theoretical calculations for normalization. The present values agree well with the various three state close coupling calculations but disagree with the six-state close coupling calculations as well as all previous experimental values which were normalized to the Born approximation calculations.

The spin-forbidden transition a 311r-x l2+ of Si0 has been observed in emission. The vibrational constants have been derived for the a 311r state. Furthermore, the energies of all the known triplet states relative to the xlX+ ground state have been obtained for the first time.

A general excitation operator of the generalized Hartree-Fock form is developed. This hamiltonian specifically includes electron-hole interaction. It is shown both that this operator possesses a Koopmans' Theorem and is based upon a variation principle.

Exact formulae for the density of the generalized oscillator strengths of the electron transitions from the 3do, 3d,l and 3dta states into continuum states with zero energy are given in the Born approximation with the Coulomb wavefunctions for electrons. The peculiarities of the generalized oscillator strengths caused solely by the angular part of initial state wavefunction are considered.

Two modifications of the Kohn variational method have been introduced by Malik and Rudge in order to eliminate certain difficulties and inconsistencies. It is shown that these two methods are in fact equivalent.

The cross section for collisional destruction of metastable hydrogen by helium has been measured for velocities between 4 x lo6 and 5 x lo8 cm s -l . Cross sections at 43 individual velocities have been obtained by an experimental method which combines time-of-flight techniques with a new kind of gas target pressure modulation. Results are compared with the existing rather elaborate theoretical work on the problem as well as with the limited experimental information.

We have extended recently reported hyperfine structure studies of 2D states in alkali atoms to several new states. The 2D states were populated in a two-step excitation scheme, involving a conventional RF lamp and a cw tunable dye laser. Using level crossing and optical double resonance techniques we have determined the hyperfine structure of the 8 2D3/2,5/a states in 8TRb and the 11, 12, 13, 14 aD3/a,5/a states in 133Cs. Further, g, factors for several of these states were determined.

The principle of a laser experiment leading to line-profile and line-shift studies is presented. The experimental set-up is largely described to show how to obtain most of the advantages of this high-resolution spectroscopy method without apparatus-function.

A high-resolution spectroscopy method is used to study broadenings and shifts in the 3.36 mu m line of xenon versus pressure of noble gases. In the case of Xe-Xe collisions, non-linear pressure broadenings and pressure-shifts appear at low densities. Experimental results are compared with semi-classical calculations using a Van der Waals potential and atomic wavefunctions of xenon. A Lennard-Jones potential is then considered.

Calculations of first-order relativistic Z-expansion coefficients are extended to states in the He and Li isoelectronic sequences containing 3p and 4p electrons. It is noted that the Briet interaction contributes only through exchange terms when dealing with the jj-configuration average of two non-equivalent electrons. Second-order coefficients for excited two-electron states are extrapolated from the variational calculations of Accad et al. (1971). Z-expansion predictions of the 1s²np ²P doublet splittings (n=2,3,4) are compared to experimental and to other theoretical results.

Coster Kronig (f₁₂) and fluorescence ( omega ₁)L₁ subshell yields of tungsten, rhenium, iridium, gold and thorium have been determined by comparing the relative intensities of the L₂ satellites with the L₁ and L₂ X-ray lines.

For pt. II, see abstr. A75105 of 1973. It is demonstrated that anisotropies can exist in the angular distributions of dissociative ions produced from a polyatomic molecule by electron impact. In particular, the distributions of O⁺ and CO⁺ ions from CO₂ are found to exhibit anisotropies for incident electron energies close to their respective production thresholds. The same symmetry arguments previously used to qualitatively explain similar anisotropies in the case of diatomic molecules can also be used in this case. The C⁺ angular distribution is found to be essentially isotropic. The cross sections for the production of CO₂⁺, CO⁺, O⁺ and C⁺ are obtained for incident electron energies up to 300 eV. Large discrepancies exist between these cross section values and those obtained in other recent experiments. It is shown that predissociation via the C state is not a dominant mechanism for the production of fragment ions.

The electron-hydrogen ionization cross section has been calculated in a 1s2s2p pseudo-state approximation at impact energies of 20.4, 27.2, 54.4 and 81.6 eV. Excellent agreement is attained with the experimental curve of Fit and Brackmann (1958) at impact energies up to 27.2 eV while above 27.2 eV the pseudo-state curve falls monotonically with increasing impact energy from their experimental curve. Comparison is also made up to 23 eV impact energy with the more recent experimental result of McGowan and Clarke (1968) where detailed agreement is not so good.

Cross sections are calculated for elastic and superelastic (including spin-flip) collisions with the first excited state of sodium, for transitions between the first three excited states, and for transitions between the fine-structure states of the 3p and 3d doublets, from reactance matrices calculated in a four state (3s-3p-3d-4s) close coupling approximation.

Total chemiionization cross sections have been measured at thermal energy (0.06 eV mean energy in the centre of mass reference frame) for collisions of helium 2¹S and 2³S metastable atoms with Ar, Kr, Xe, N₂, O₂, NO, CO, CO₂, N₂O, and CH₄, using a crossed beams technique. The results in several cases are in disagreement with earlier published values. A careful analysis of the various data has not revealed the cause of the discrepancy.

Collision strengths for exciting Li⁺, be⁺⁺ and O⁶⁺ from their ground states by electron impact have been computed using the Coulomb Born approximation. Results are given for excitation to the levels n¹S and n¹P (n<or=6). The initial and final target states were approximated by frozen-core Hartree-Fock wavefunctions. Dipole length oscillator strengths for the transitions 1¹S to n¹P have also been calculated.

The absorption of the principal series of calcium is observed with approximately=4% of the atoms placed in the 4s4p ³P level by selective laser excitation, and is compared with the absorption with all atoms in the ground state. A broadening of the absorption lines accompanied by a shift to longer wavelengths and the occurrence of satellite lines at shorter wavelengths were observed.

The vibrational excitation and dissociation probabilities of H₂ in a collinear collision with He are calculated, using the semi-classical time-dependent method along with the accurate H₂ molecular potential of Kolos and Wolniewicz (1965, 1968). The complete set of bound and continuum eigenfunctions are represented in terms of a truncated basis set of harmonic oscillator functions. The results differ significantly from the Morse potential quantum mechanical calculations of Clark and Dickinson (1973). In addition, a state-dependent interaction potential is suggested to allow for the different average sizes of the H₂ molecule in its initial and final states. The state dependent potential greatly enhances the transition probabilities to highly excited states and the continuum.

The energy values of some doubly ionized states of CH₄, N₂O, C₂N₂, C₂H₂, C₂H₄, C₂H₆, C₃H₈, C₆H₆, CH₃OH are determined by measuring the translational energy spectra of H^- ions arising from single collision double charge transfer of 4 keV protons on these molecules. Assignments of the measured values to given states of the doubly ionized molecules are discussed. A comparison of the ionization potentials of the neutral and singly ionized molecule is made for some of the molecules.

Rotational structure in five bands, viz (0,0)_1/2, (0,1)_1/2, (0,1)_3/2, (1,0)_3/2 and (0,2)_3/2 of the B-X system of the silicon monochloride molecule has been analysed by photographing the spectra in the third order of a 10.6 m concave grating spectrograph (dispersion 0.22 A/mm). The rotational constants of the states participating in the transition are obtained as follows: B_e'=0.2791+or-0.0003 cm^-1; D_e'=1.8*10^-7 cm^-1; alpha _e'=0.0020 cm^-1; B_e"=0.2561+or-0.0001 cm^-1; D_e"=2.30*10^-7 cm^-1; alpha _e"=0.0015 cm^-1; lambda -type doubling in the ² Pi _1/2 component=0.006 cm^-1. The spin splitting in the excited state is found to be of negligible magnitude. The weak isotopic lines due to ³⁷Cl have also been detected.

Elastic scattering of electrons by neon and argon atoms and hydrogen molecules are considered in the plane wave approximation. Comparison of the present results with the available experimental data indicates that the polarization potential is of importance even up to incident energies as high as 800 eV.