Table of contents

It is pointed out that, for neutral atoms, all-external correlation effects are important in the calculation of oscillator strengths. It is argued that some recent values obtained by Nicolaides et al (1973) for oscillator strengths in neutral Be may be in error.

Integral functions and perturbation theory are used for estimating the magnitude of the Heisenberg uncertainty in simple atomic systems.

The angular distribution for the elastic scattering of 50 eV electrons from atomic hydrogen has been measured in the angular range 15 degrees to 130 degrees . The results are compared with those predicted by the Glauber approximation, the close coupling approximation, a multiple scattering approximation, the plane wave Born approximation, and a second order potential approximation. None of these approximations agree with the measured data over the whole angular range.

A detailed study has been made of the 3s3p⁶np ¹P and 3s3p⁶nd ¹D autoionizing resonances in Ar using a high resolution electron spectrometer. Positions and widths of the features are presented and compared with the results of other workers and with theory.

The peculiar accuracy of the expectation value ( Sigma r_j^-1) as computed by first order perturbation theory is explained. Relationships between various energy expectation values in perturbation theory are used to give a check on variational calculations for the configuration 1s2p.

Stimulated emission and absorption have been simultaneously observed in the profile of the 3.36 mu m line of xenon in presence of krypton. Some aspects of the phenomenon can be explained with the simple assumptions of a weak difference of temperature between the two levels.

Photoabsorption coefficients of molecular nitrogen have been obtained to +or-3% accuracy in the 380-700AA region using a synchrotron radiation source and channel electron multiplier photodetection. Broad structure in the continuum is clearly observed with an absorption maximum at 540AA and a shoulder at 430AA.

Small changes of approximately 2 to 3 deg in the angle between a magnetic field and the axis of a discharge tube containing a decaying rare gas afterglow cause a change of between 200 and 300 per cent in the electron decay time.

Auger spectra of Ar(L_2,3M_2,3M_2,3) excited by 860 eV electrons were measured by a high resolution and variable angle electron spectrometer. At larger angles, the present spectra agreed with the measurements by Siegbahn et al and Mehlhorn et al, whereas at smaller angles, four extra peaks were discovered. The level width of the L₂ was found to be equal to that of the L₃ which was 0.10+or-0.02 eV on the basis of the line width measurements of each peak at the highest resolution (40 meV) of the spectrometer. The transition probability of Ar L_2,3M_2,3M_2,3 (¹D₂) was estimated as (1.5+or-0.3)*10¹⁴s^-1, which coincided with Rubenstein's calculation.

An expansion of the perturbed atomic state wavefunction in terms of R-matrix states is used to calculate the dynamic dipole polarizability alpha ( omega ) of the ground ¹S state of the beryllium atom and the ground ³P state of the carbon atom. The effect of including configuration interaction in both the ground and perturbed state wavefunctions is studied. The corresponding Van der Waals C₆ coefficients of the long-range interaction between two ground state beryllium atoms and between two ground state carbon atoms, are also calculated.

Calculations of radial momentum distributions and Compton profiles have been carried out, in the framework of the impulse approximation with a variational formalism, which gives about 98% of the correlation energy for the (¹S) Be and (¹S) Ne atoms in their ground state. It is shown that the corrections to the Compton profiles and radial momentum densities due to the electron correlation are not always negligible, even though these quantities are related to one electron operators, and that these effects must be taken into account in order to compare with increasingly precise experimental results.

The coupled equations of the adiabatic-state expansion formulated in the context of the stationary-state scattering theory are examined. The translational factors are introduced in the eikonal approximation through coordinate transformation. The equations are consistent with those of Chen and Watson (1968) in that they are free from the spurious long-range interaction even in the absence of the translational factors. The cancellation of the spurious R^-1 long-range interaction of the 2p sigma _u-2p pi _u rotational coupling in the (p⁺,H) system is given as an example. The effect of the translational factor on the channel coupling interaction is discussed.

The conditions under which cross sections can be scaled from calculations on a one-electron system are investigated. The conditions are found to be met in the case of K-shell excitation in low-velocity symmetric ion-atom collisions. Cross sections for K-shell excitation in first row atoms are calculated in this way and are found to be in good agreement with existing measurements.

A theory is derived which accounts for the asymptotic effects of all Coulomb potentials occurring in the process of electron detachment from singly charged negative ions when olliding with charged particles. The T-matrix element of this process is redefined in a way which makes initial and final channel states asymptotically identical to the outgoing and ingoing scattering wavefunctions respectively. Calculations of doubly differential, simply differential and total cross sections with proton impact are compared with the results given by the Born approximation.

Cross sections for elastic scattering and excitation of the resonance transitions in Li, Na and K are calculated in the frozen core Glauber approximation. The total cross sections for the resonance transitions are observed to be in quite good accord with available experimental data. The importance of including the effect of the core electrons in the elastic scattering calculations is stressed. The first Born approximation for elastic scattering from Na and K is found to be in considerable error for the energy range studied (1 eV to 1 keV). Theoretical total cross sections calculated by adding experimental resonance cross sections to the Glauber elastic results agree reasonably well with experimental data. Glauber and first Born differential cross sections are also presented.

The continuum distorted wave method is applied to study electron capture collisions of fast alpha particles with hydrogen and helium atoms. The cross sections for capture into 1s, 2s, 2p, 3s and 3p final states are calculated in the energy range of 25 keV to 3 MeV. Necessary extensions of the method are done in order to treat capture to excited states.

The effect of many-electron correlations in the inelastic electron-atom scattering at high energies is investigated. The importance of these correlations is shown by comparison of the results of calculations with the best possible independent particle model and the experimental data. Many-electron correlations are included in the random phase approximation with exchange (RPAE) and the corresponding integral equation for the effective interaction is displayed. This equation has been solved numerically for argon, and generalized oscillator strength densities as well as the differential cross section were calculated. The results agree with the experiment quite well, showing thus the very important role the many-electron correlations play in the inelastic electron-atom scattering. The calculations confirm the relative importance of the monopole and the quadrupole transitions in the process under consideration.

A comparison is made between 'Born' and 'binary-encounter' generalized oscillator strengths of the continuum states of hydrogen for hydrogen atom impact. The results of this comparison show that resonance excitations are less important for ionization by hydrogen atom impact than for ionization by proton impact and that, consequently, the Born and binary-encounter approximations will be in closer agreement in the former case than in the latter case.

A theory of spectral line broadening in plasmas which accounts for the ion dynamic broadening is reviewed and modifications are made to achieve a form which is amenable to calculation. The calculational procedure is discussed. The results are compared with other theories of spectral line broadening in plasmas and experimental data. A brief discussion is given of the alternative methods used to introduce ion dynamics into line broadening formalisms.

For pt. I see ibid., vol.6, 1044 (1973). Calculations of the plasma broadened H_beta profile including ion dynamics are presented. The effects on the line profile of the random phase approximation for the plasma subsystem is examined. Comparisons are made to theory and experiment and a discussion of the asymmetry of the profiles is given.

Using a single-collision beam technique, cross sections have been measured for the detachment of electrons from O^-, O₂^-, O₃^- and NO₂^- ions in oxygen, nitrogen and dry air, for NO₃^- in oxygen and nitrogen and for CO₃^- in oxygen. The ions were obtained from highly ozonized oxygen in an electron bombardment source and the ion energy range was from 20 to 100 eV.

The wavelengths of components of the Balmer- alpha line in dueterium and tritium have been determined in terms of the ⁸⁶Kr 606 nm primary standard to establish a value for the Rydberg constant. Improved resolution of the fine structure was achieved by using a discharge cooled in liquid helium to reduce the Doppler width. Positions and intensities of the fine structure components were found by analysis of the spectral line profiles. Variation of the discharge conditions produced no effects which could be correlated with predictions of Stark effect theory. The fine structure of tritium was found to be the same as that of deuterium to within experimental error and the isotope shift was satisfactorily described by the reduced mass factor. The value of the Rydberg constant was found to be R_infinity =109 737.326+or-0.008 cm^-1. The estimated error is to be understood as one standard deviation. The result is based on measurements of the three strongest components in the deuterium fine structure.

The determination of the Rydberg is based on the measurement of the wavelengths of suitable fine structure components in the spectra of one-electron atoms. A source of possible systematic error is the Stark effect arising from electric fields present in the discharge tube. A detailed analysis is given of the stark effect on the Balmer- alpha line of the isotopes of hydrogen. The frequency shifts and intensity changes are displayed for values of the electric field from 0-300 V cm^-1.

For pt. II see abstr. A31645 of 1972. The author solves the problem of a strong RF field interacting with a degenerate doublet in terms of complex order Bessel functions. The influence of phenomenological pumping and decay parameters is displayed. The solution is compared to numerical results obtained from the previously published continued fraction solution.

Helium singlet and triplet metastable densities have been measured by a line absorption technique in a 3 mm bore capillary tube over the pressure range 0.5-15 Torr and current range 10-200 mA. With constant discharge current the singlet and triplet densities show pronounced maxima of 2*10¹² cm^-3 and 9*10¹² cm^-3 respectively at about 2 Torr. At constant pressure the metastable densities saturate for currents above approximately 20 mA. Experimental values are in fair agreement with those calculated using known cross sections for production and loss mechanisms. The addition of cadmium vapour to simulate the conditions of laser oscillation at 4416 AA and 3250 AA in Cd II has two principal effects; cadmium vapour reduces the metastable populations-almost halving them when the optimum cadmium pressure for lasing is reached, and further the metastable densities now saturate at much higher currents (60-120 mAA). The observed optimum performance of the He-Cd laser with respect to discharge current, helium filling pressure and cadmium partial pressure is related directly to the behaviour of the helium metastable densities as these parameters are varied.

The thermal diffusion coefficient for electrons in helium at room temperature has been measured in order to obtain an independent check of experimental and theoretical momentum transfer cross sections that have recently been published. An adaptation of Cavalleri's method was used which avoids the possibility of errors due to drift induced by surface potentials within the diffusion cell. The value of the diffusion coefficient obtained confirms the cross section derived from other transport data and indicates that the theoretical cross sections are about 5% low. The fact that the measurement is made in the absence of an electric field makes this confirmation particularly valuable since the determination of the cross section does not rely on approximations that are usually made when transport theory is applied to make a similar determination from mobility measurements.

The change in the signal absorptions by rare gas afterglow plasmas as a DC magnetic field is varied in the range 0-400 G is studied in the frequency range 200-1500 MHz. The measurements are made using large aluminium cavities excited in the TM_0m0 family of modes with a uniform DC magnetic field, B, applied along the direction of the alternating electric field. Signal absorptions are observed to occur, B=0, at several successive times during the afterglow for signal frequency, f_M, when the pulsed plasma is excited by means of an 8 ms pulse of high frequency energy at 54 MHz. The absorptions get smaller as the magnetic field is increased slowly in magnitude, and disappear, in turn, for certain critical values of field, B_crit. Plots of f_M against B_crit fall on straight lines having almost integrally related slopes, the lowest slope having a value close to 2.80*10⁶ HzG^-1 in magnitude. The phenomena are believed to be explicable in terms of the oscillations of a low energy gas of electron pairs which break up at critical values of B. The plasma oscillations of a free electron gas are also briefly discussed.

The reduced mobility of K⁺ ions in He, Ne, Ar, H₂ and N₂ and in mixtures of He-Ne, Ne-Ar and H₂-N₂ has been measured at 293 K over the range 20<or=E/N(Td)<or=100 using the Bradbury-Nielsen time-of-flight technique. A theory has been developed which predicts the deviations from Blanc's Law in situations where only elastic scattering occurs. The measured deviations in mixtures of He-Ne and Ne-Ar are in good qualitative agreement with the predictions of this theory. In H₂-N₂ mixtures the measured deviations are of opposite sign and differ in magnitude from the predictions of the recent theory of Mason and Hahn (1972). The measured values of the reduced mobility of the ions in the pure gases are estimated to be in error by less than +or-2% over the whole range of E/N and the errors in the measured deviations from Blanc's Law are considered to be less than +or-0.4%.