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The method involves the application of a depolarizing magnetic field at the 'no-polarization' angle of 54.7 degrees to the electric vector of the optical resonance excitation. The decay of fluorescence following a pulse of excitation then gives gamma ₀ directly. Application is made to the 5³P₁ state of cadmium.

The energy for the three-particle ground state of the (e^-, He⁺) system, namely that of the helium atom has been calculated using Faddeev theory and following the method of Ball et al. (1968). Retaining only 1s and 2s terms in the Sturmian set of expansion for two-body collision amplitude, the result is found to be in good agreement with experimental measurement.

A non-relativistic Hartree-Fock self-consistent procedure has been used to investigate some properties of the argon atom and its ions. The electronic binding energies of the various sub-shells have been calculated for both single and double hole states. The energy of the X-ray photon and Auger electron associated with the filling of a vacancy in the L shell has been calculated. The incident- ion energy-dependent line shifts observed in the X-ray and Auger- electron emission spectra obtained from Ar⁺-Ar collision studies are explained in terms of the filling of the L₂₃ single vacancy in argon ions with different numbers of valence electrons.

For pt.I, see ibid., vol.4, 1 (1971). The electron binding energies for the various sub-shells of the neon atom and its ions have been calculated using a non-relativistic Hartree-Fock self- consistent field procedure. The dependence of the energy of the emitted X-ray photon or Auger electron when a K-shell vacancy is filled on the degree of ionization in the valence shell of the atom has been investigated. Both single and double hole states have been considered.

The simple operator gamma N.S which is usually assumed to give a proper description of the first order spin-rotation interaction in diatomic molecules, is in the case of Sigma states shown to be strictly derivable from a fundamental microscopic Hamiltonian given by Van Vleck. In this derivation the electronic screening of the rotating nuclear charges is taken into account. For other types of states it is emphasized that this simple operator only represents an approximation to the true spin-rotation interaction Hamiltonian. Assuming the electronic functions to be given by a Slater determinant of one-electron molecular orbitals, a formula suitable for ab initio calculation of the coupling constant gamma is derived.

A new method of derivation of operator equivalents is proposed, in which individual irreducible tensor components are expressed in terms of both real and complex unit tensors derived from real and complex (or bi) vectors. The method is extended to irreducible tensor operators which do not have full permutation symmetry and it is found that these are equivalent to totally symmetric tensor operators of rank equal to the angular momentum quantum number.

For pt.I, see abstr. A43029 of 1970. The upper-bound property of the multiconfiguration energy-bound method has also been tested for Feshbach-type autoionization states lying between higher excitation thresholds of one-electron targets. As an illustrative example more compound states associated with the ¹S^e closed-channel (Feshbach) resonances for the (e, He⁺) scattering system lying between the n=2 and n=3 thresholds, and between the n=3 and n=4 thresholds, have been calculated. The best results so far obtained variationally of the energy positions and the corresponding wave functions are given in the present paper.

A relation is derived between unitary transformations in the impact parameter approximation or in the classical path method. The unitary transformations describe the behaviour of the electrons before and after the trajectory, which is followed by heavy particles, crosses the turning point. The properties used to establish the relation are the assumption that the trajectory of heavy particles is determined by a spherically symmetric potential as well as the invariance of the Hamiltonian under rotation and the time inversion invariance. To facilitate the use of this relation an additional relation is derived using the fact that a trajectory determined by a spherically symmetric potential is constrained to a plane.

The vibrational excitation of N₂ molecules by resonance scattering of electrons of 2-3 eV is calculated with a compound state model, that is on the assumption that the mechanism is e+N₂ to N₂^- to N₂+e'. The complex electronic energy of the N₂^- ion is treated parametrically, the essential new point being that Gamma /h(cross), the autoionization rate, varies with the separation of the nuclei. The variation comes from the dependence of the angular momentum barrier on the energy of the emitted electron. Good agreement is obtained with the experimental energy dependence of cross sections with reasonable values of the parameters. Calculations have also been done to illustrate the transition to the impulse limit as Gamma is increased, and to the compound molecule limit as Gamma is reduced.

Angular distributions of electrons resulting from exchange scattering on the ground state of the hydrogen atom are calculated in the distorted wave approximation in the energy range 1 to 50 ryd. Comparison is made with various plane wave approximations and with the close-coupling calculations of Burke, Schey, and Smith (1963). It is found that the distorted wave results are in much better agreement with the close-coupling calculations than are the plane wave results. It is also found that inclusion of a static polarization potential does not greatly affect the distorted wave results in this energy range.

The usefulness of three methods of approximation which include second order effects for the calculation of intermediate and high energy scattering cross sections is studied. They are tested in potential scattering and then are applied to the elastic scattering of electrons and positrons by hydrogen atoms, including as second order corrections the transition through the 1s, 2s and 2p intermediate states. It is found that the Pade method is reliable over a wider energy range and inconsistencies are shown in the third order approximation usually employed in the evaluation of e^+or--H scattering.

Cross sections of the reaction H^-+e to H⁺ +3e have been measured for interaction energies between threshold (14.4 eV) and 850 eV. The cross section reaches a maximum value 5.0*10^-17 cm² at 70 eV. Comparison with previous measurements shows that, for energies greater than 100 eV, the ratio of cross sections for single and double detachment is almost constant and equal to 39+or-10%. The present measurements are compared with similar results for helium and Li⁺.

A modulated beam technique has been used to investigate the collisional destruction of 10-30 keV 2s metastable hydrogen atoms in passage through hydrogen, helium, neon, argon, krypton and nitrogen. It is shown that, at the impact energies investigated, both electron loss and de-excitation are significant destruction processes and the absolute cross sections for each process have been separately determined. Loss cross sections for metastable atoms, which were found to be approximately a factor of two larger than the corresponding cross sections for ground state hydrogen atoms, are compared with recent theoretical estimates obtained by Bates and his collaborators using a classical impulse approximation. The formation of metastable atoms by charge transfer neutralization of 10-30 keV protons has also been analysed quantitatively using neutralizer gas pressures high enough to obtain equilibration of the beam.

The decay in flight of He^- ions has been studied under field free conditions. Measurements with He^- beams of energies between 2 and 30 keV in flight tubes from 0.1 to 1.7 m long have established the existence of two components with greatly different lifetimes present in approximately equal proportions in the beam. The lifetime of the long lived component appears to be comparable with that predicted theoretically for the ⁴P_5/2 state while the second component, which dominates the observed decay, has a lifetime of 9_-3⁺⁵ mu s.

Cross sections of one-, two- and three-electron loss processes for C^- and O^- on Ne, Ar, Kr, Xe and N₂ were measured over an energy range of 5-30 keV, using a beam technique. One-electron loss cross sections sigma ₁₀ varied in the range of 10^-16-10^-15 cm², while two-electron loss cross sections sigma ₁₁ were found to be for an order of magnitude lower than sigma ₁₀, in the present energy range. Three-electron loss cross sections sigma ₁₂ increased sharply with the incident ion energy and their values ranged from 10^-20 up to 10^-17 cm². The dependence of the measured cross sections on gas target mass number, incident ion characteristics and energy is discussed.

Optical second-harmonic generation coefficients have been measured for several organic molecular crystals. Variations in coefficients for related compounds can be correlated with differences in molecular structure. Highly polarizable aromatic molecules with substituent groups arranged to produce a large static polarization are relatively efficient non-linear optical materials. Acentric alternant hydrocarbons have low coefficients, but if the alternancy property is broken down by substitution they behave normally. A method is described which will permit rapid evaluation of some non-linear coefficients for low-melting materials.

Using high resolution spectrograms, the broadened linewidths for several bands of the B ² Sigma ⁺-A ² Sigma ⁺ system of OD have been reinvestigated. Comparison between observed and calculated halfwidths shows that the high-vibrational level predissociation is a case c⁺ one, due to a first order spin orbit interaction, with a repulsive ⁴ Pi state which crosses the A ² Sigma ⁺ state of OD at r=1.65 AA between v=7 and v=8, and between v=5 and v=6 for OH. The vibration- rotation interaction is shown to be responsible for the strong halfwidth dependence on the rotational quantum number.

New spectra have been obtained for Zn-Tl and Cd-Tl mixtures excited by a high frequency oscillator and studied under a dispersion of 5 AA mm^-1. Both the mixtures show one system in the red, one in the blue and continuous bands attached to the Tl lines 3775 and 5350 AA. The red system of Zn-Tl mixture exhibits an isotope effect, which shows ZnTl₂ as the emitter and for the red system of Cd-Tl mixture CdTl₂ is the emitter. The blue systems and continuous bands are due to diatomic ZnTl and CdTl molecules. A vibrational analysis of all these systems has been carried out wherever possible and the constants determined.