Table of contents

The two-potential formula of scattering theory is used to determine the low energy scattering by long range potentials having the asymptotic form r^-3. An interaction of this form occurs between two identical neutral atoms which are excited to different degrees. The author calculates tan delta ₀ up to and including the k⁴ term and, for L>0, we calculate tan delta _L up to and including the K^2L+1 term.

New spectral data on the comet tail system of CO⁺ indicate that the electronic transition moment of this system is constant or slowly varying for internuclear distances between 1.07 and 1.19AA. This conclusion is supported by the life-times of the vibrational levels of the CO⁺ A² Pi state.

The photodetachment cross section of Li^- is calculated by the Bethe-Longmire method.

Radial wavefunctions consisting of two exponentials are proposed to approximate 3d orbitals throughout the iron group series for the 3d^m4s¹ configuration. The simple form and dependence on atomic number of the functions makes them adapted for any application to molecular and solid state physics.

For original article see abstr. A31798 of 1972. Rundel recently cast doubt on the accuracy of some theoretical and experimental cross sections for the production of protons by collisions between electrons and H₂⁺ ions. Some reasons are listed which lead the authors to reject Rundel's arguments.

The doubling in 3C states may be used to determine the separation of the Q = 1 and 52 = 0 sub-states. Measurements of bands of the AI-Xl system have been used to derive an estimate of the 1 -0+ separation in the ground state of TeO as 679+ 15 cm-l.

The matrix element for transition from ground state to final continuum state for atomic hydrogen in the presence of an intense electromagnetic field is calculated.

A one parameter function is presented as an approximation to the ground state wavefunction of the two electron radial hamiltonian. The parameter may be fixed by a non-variational criterion. The resulting expectation value of the radial hamiltonian differs from its exact eigenvalue by about 2 parts in 3000 for helium while the 'local energy' never differs by more than 10% from the exact value over the entire r₁-4₂ plane. The cases Z=1 and Z=3 are also investigated.

The second order energy of an atom in an expansion in which the interelectronic interaction is treated as a perturbation can be written as a sum of certain partial sums. Each partial sum represents the contributions of the zero order states originating from a fixed excitation of one electron and an arbitrary excitation of another electron. A method for the exact analytical evaluation of a certain class of such partial sums is developed. The relevance of the method to the calculation of the correlation energies in atoms is pointed out. The advantages and the disadvantages of the method in comparison with some other methods are discussed.

Quantum mechanical sum rules and results from the theory of moments are employed in the construction of rigorous upper and lower bounds on the mean energies of stopping, straggling, and molecular excitation appropriate for the passage of fast charged particles through matter. The bounds are constructed with effective excitation spectra chosen to satisfy known oscillator strength sum rules, in accordance with the dictates of the theory of moments, thereby circumventing the formally required spectral distribution of dipole oscillator strengths. Accurate results are obtained in the cases of atomic and molecular hydrogen and the inert gases with a minimum of computational effort, demonstrating that the moment theory approach for determining charged particle mean penetration energies compares favourably with ab initio theoretical, semi-empirical, and closely related linear programming methods.

The ¹P to ³P separation has been determined by minimizing the energies of the two states explicitly in the Hartree-Fock procedure and then taking the difference of the total energies determined for the two terms. This procedure gives extremely accurate results for K II and Rb II. The accuracy diminishes for more highly ionized atoms, but is still considerably better than that found using the conventional approach. The results of the Hartree-Fock calculations turn out to be qualitatively different for K II and Ca III (Rb II and Sr III). For K II, the ¹P term is calculated to be below the prediction made by the usual approach in all 3p⁵nd configurations. In Ca III this result holds for the 3p⁵3d configuration, while the calculations show the opposite result for all higher configurations. The reasons for this difference are discussed.

Recently discrete resonances in the photoabsorption spectrum of La near the 4d electron threshold have been identified as combinations between the ground-state of La IV, 4d¹⁰5s²5p⁶¹S₀, and the J=1 levels of the 4d⁹5s²5p⁶4f configuration, the strongest combination being with 4d⁹4f¹P₁. The agreement was satisfactory between energies from observations and from ab initio calculations except for ¹P₁, for which the energy predicted by using wavefunctions determined for the mean energy of the whole configuration is about 14 cV too high. The present Hartree-Fock calculation for the ¹P term removes half of this discrepancy. Part of the remaining discrepancy may be caused by solid state effects. The relevance of this result for calculations of photoionization in Ar I and Xe I is pointed out.

A detailed analysis of the IOC- omega technique (inclusion of overlap charges in omega technique) has been presented. An attempt has been made to derive it from the Roothaan equation with systematic approximations and explain the reasons for its success.

An alternative form of building up the terms associated 'modified Aufbau procedure' requires less ad hoc assumptions states of the elements of the periodic table is established. This modified Aufbau procedure' requires less ad hoc assumptions than the (n+l,n) recipe. It furthermore allows one to relate the atomic magic numbers to the degeneracies of irreducible representations (IR) of a group built as the direct product of three SU(2) groups, making for a better theoretical understanding of the periodicity of the elements.

The multiconfiguration energy bound procedure has been applied to Feshbach-type autoionization states with the ^1.3P^e symmetries of He. The calculations were performed in connection with an investigation of a possible extension of the MCEB procedure to include also the nonphysical intersections of roots originally belonging to different thresholds. The resulting curves exhibit only single minima. The nonrelativistic energies are given for some of the lowest lying states of both symmetries pertaining to the n=3 and n=4 thresholds. The correct identification of the various curves is facilitated by the computed contributions to the total wavefunction from the different types of configurations.

Auto-ionization energies of He and H^- converging on the n=3 and n=4 hydrogenic thresholds are computed for states of several different symmetries by using the Feshbach formalism. Eigenvalues of the appropriate QHQ operator are determined by the Rayleigh-Ritz variational method. The trial wavefunction consists of an expansion in terms of the products of hydrogenic states and the exponentially decaying functions. Comparison is made with the experimental results and with other theoretical studies.

Information on both the relative magnitudes and phases of the various scattering amplitudes can be obtained by measuring the angular correlation of inelastically scattered electrons with the emitted photons in the electron impact excitation of atomic line radiation. As an example, excitation of sodium resonance radiation by electron impact at energies close to threshold is examined using close coupling T of Karule and Peterkop.

Kohn's variational method is used to calculate the positron-hydrogen scattering length and the S wave phase shifts at several energies below the positronium formation threshold, and good agreement is obtained with the results of other recent variational calculations. A detailed analysis of the structure of the zero energy wavefunction is made, and the wavefunction is used to calculate the electron-positron annihilation rate parameter Z_eff, with the result 8.9, and the angular correlation of the two annihilation gamma rays. The energy dependence of Z_eff is also investigated using the positive energy wavefunctions.

The third harmonic generation coefficient of the hydrogen atom is calculated using the sturmian coulomb Green function. The calculations of the nonlinear optical constants have been stimulated by recent developments in laser physics.

The cross sections for singly stimulated two-photon emission and anti-Stokes Raman scattering from the 2¹S₀ metastable state of helium care calculated by a variational procedure for incident photon wavelengths in the range from 5000 AA to 50 mu m.

Electron impact ionization of boron, carbon II, Nitrogen III, and oxygen IV, in their ground state configuration 1s²2s²2p, is treated, where allowance is made for inner shell ionization. Partial wave cross sections were calculated using both the so called 'modified' coulomb Born and the coulomb Born exchange approximation. Comparison is made with the only existing results of Peach and Lotz.

For pt. II see abstr. A6932 of 1972. Measurements have been made of the angular and energy distributions of electrons ejected from contaminated metal surfaces due to thermal energy metastable rate gas atom impact. Mechanisms are proposed to explain these observations and also the high values of secondary emission coefficients previously measured. The secondary electron yield was found to be approximately independent of the angle of incidence of the metastable atoms. Reflection coefficients for metastable atoms at contaminated metal and glass surfaces were found to be very small and no ion emission was observed.

Nitrogen at approximately atmospheric pressure is 'seeded' with small amounts of potassium vapour and heated to approximately 1300K in a specially designed furnace. The microwave propagation characteristics of the thermal plasma thus produced are measured using a very sensitive microwave bridge and the DC conductivity of the plasma is determined using a pair of electrodes of variable separation. Each of these techniques leads to a value for the collision cross section for momentum transfer of nitrogen. The means of the results obtained by each method are (7.5+or-0.6)*10^-20 m² and (6.8+or-0.3)*10^-20 m² respectively.

Total cross sections for the excitation of helium from its ground state to the 2¹P, 3¹P and 4¹P levels by electron impact have been measured in a polarization free manner using a crossed beam apparatus. The apparent excitation functions have been cascade corrected and made absolute using the optical oscillator strengths. The excitation functions exhibit shapes which differ from some other recent measurements particularly around the peak of the cross section curves. Agreement at high energies between the measured total cross section values and the Bethe approximation is verified within experimental error.

Drastic changes are observed in both the magnitude and the energy dependence of the attachment cross section, sigma _a( epsilon ), for the formation of O^-₂ with increasing N₂ density in O₂-N₂ mixtures. At low densities sigma _a( epsilon ) exhibits distinct structure attributed to electron capture into vibrational states of O₂^-.

Experimental observations of the frequency shifts of the (J,K)=(12,12) line in the inversion spectrum of NH₃ due to collisions with the foreign perturbers, He, A, CH₄, N₂, Co₂, COS, CH₃CN and CH₃F have been reported: an attempt is made in the present paper to interpret these observations in terms of the impact theory of Anderson. Dipole-induced dipole, dispersion exchange dipole-dipole, dipole-quadrupole, quadrupole-dipole, quadrupole-quadrupole, quadrupole-dipole induced dipole and dipole-quadrupole induced dipole interactions are considered: all but the first three interactions make no contribution to the line shift according to the theory, and even these give nonzero contributions only if the dipole moment and/or the polarizability of an ammonia molecule change when the molecule undergoes a transition between the inversion states. Provided the polarizability of NH₃ is greater in the upper level of the inversion doublet than in the lower, the dipole induced dipole and the dispersion interactions give shifts towards lower frequencies, in qualitative agreement with experiment, but the estimated magnitudes, with the exception of shifting by He and A, were too small by factors of up to approximately 100; the exchange interaction gives a contribution to the shift of the opposite sign to that observed.

Measurements of pre-breakdown ionization currents were carried out on samples of helium prepared in two different ways and introduced into an ultra-high vacuum system. Using the method of analysis developed previously by Dutton and Powell (1971), the results are interpreted to show that the impurity (0.9 vpm) in a sample produced using superfluid helium was lower than that (2.6 vpm) in a sample produced by allowing gas from a high pressure cylinder into the system through refrigerated charcoal traps and then running a cataphoresis discharge continuously.

Proposes two methods of band analysis each of which may be used to derive band oscillator strengths from the detailed form of a band interferogram. The methods are intrinsically more sensitive than the hook technique developed by Rozhdestvenskii and should serve to enhance considerably the versatility of the dispersion approach to molecular measurements.

For pt. I see ibid., vol. 5, 1241 (1972). The 'fringe shift' and 'fringe slope' techniques have been used to obtain oscillator strength estimates of the (0,0) band of the NO- gamma system as follows: f₀₀(fringe shift)=(4.09+or-0.1)*10^-4 f₀₀(fringe slope)=(4.33+or-0.2)*10^-4. The results are in good agreement with published absorption and hook measurements.

3pⁿ-3p^n-14s,4d and 3pⁿ3d-3pⁿ4p,4f transitions of Fe IX to XVI and Mn VIII to XV are classified through comparison of observed spectra with spectra computed using atomic self consistent field calculations. The required quality of observations was achieved by recording data during the short period when a theta-pinch emitted spectra from the ionization stages under investigation. Accurate wavelength measurements in iron permit correlations to +or-0.02AA with lines in the solar spectrum between 60 and 120 AA. Observations of emission lines from these configurations were previously seriously deficient.