Table of contents

See abst. A60953 of 1971. It is shown that, of lower bound formulae depending on the variance, the bound of Temple is to be preferred. The conclusions of Cohen et al. concerning the accuracy of the 'frozen-core' wavefunctions for two-electron atoms are not justified on the basis of their lower bound calculations.

Simple algebraic equations for cross sections for excitation by fast protons of H atoms to np or nd states have been obtained. The equations are applicable for incident energies not less than 25 keV.

The correspondence principle for strongly coupled states is used to obtain approximate transition probabilities for a forced harmonic oscillator. For particular forcing potentials, of interest in the vibrational excitation of molecules, the results are shown to be valid even for low order transitions.

Semiclassical values for the numbers and density of bound states of the screened Coulomb potential are compared with quantum mechanical results. Good agreement is found in some cases but there is disagreement with the recent values of Preist for the total number of bound states. The accuracy of the semiclassical values has been confirmed by sample checks using an alternative method of solving the quantum mechanical problem. The regions of energy and angular momentum where quasi-bound states of this potential may occur are discussed.

It has been considered that Pradhan's impulse approximation is not valid for H⁺+H to H+H⁺ in high energy range (above 200 keV). However, it is found that this discrepancy comes from simple numerical errors and Pradhan's approximation shows proper energy dependence in high energy limit as well as absolute values.

The continuum-distorted wave method is used to calculate cross sections for electron-capture by protons in atomic hydrogen in the energy range 50-400 keV. The theoretical results are compared with the experimental ones and the agreement is seen to be very satisfactory.

The continuum-distorted wave method is applied to the calculation of the cross section for the production of H^- by electron capture in H-H collisions. The energy range is 5-70 keV. The theoretical results are compared with the experimental results of McClure.

Electric field induced anticrossing signals are used to measure the fine structure splittings S-F of n=4 in (⁴He)⁺. The crossing positions have been extrapolated to zero electric field. The present results are (27435.7+or-13.8) MHz for the interval 4²S_1/2- 4²F_5/2 and (31098.8+or-10.5) MHz for the interval 4²S₁2/-4²F_7/2 in agreement with the theoretical values of (27466.99+or-1.36) MHz and (31104.78+or-1.36) MHz respectively. The interval 4²F_5/2-4²F_7/2 is derived to (3663.1+or-24.3) MHz compared with (3657.78+or-0.01) MHz from the theory.

For pt. II see ibid., vol.4, 1388 (1971). Numerical estimates of the Trees parameters alpha , beta , gamma for Pr²⁺ (4f³) are reported. Configuration interactions through second order excitations to bound states are considered in detail. It is shown that excitations of the type 4d to 4f and 4f to 5d are dominant. The results are compared with recent work on Pr³⁺. Bound state excitations alone grossly overestimate the parameters for both ions. Introduction of a screening factor of ¹/₅ for the excitations of two 4f electrons from d states gives reasonable agreement with experiment. Excitations to the continuum are crudely estimated but they do not appear to give sufficiently large corrections to the values of alpha , beta and gamma to lead to good agreement with experimental data.

For pt. III see abstr. A14127 of 1970. Multiconfiguration Hartree-Fock calculations are given to study term-splittings, electron-affinities and ionization energies for the 2p³ isoelectronic series (Z=6.0 to 30.0) and 2p⁴ series (Z=7.0 to 30.0). The contribution to the correlation energy of the configurations used has also been analysed. The predicted multiconfiguration Hartree-Fock term splitting ratios for the 2p³ configuration are in good agreement with experiment and in much better agreement than the Hartree-Fock values. This is also true for the individual ⁴S-²D and ⁴S-²P transition energies. For the 2p⁴ series, the predicted term splittings are not as good as for the 2p³ series. Ionization potentials for the 2p³ and 2p⁴ series, are given up to Z=30. The computed ionization potentials and the electron affinities of C and N are compared with experiment. The Z dependence of the computed ionization potentials is discussed. The results are not in as good agreement, relatively, for the electron affinities of C and N as for the ionization potentials but the absolute errors are roughly the same.

For pt. I see abstr. A57817 of 1971. Developing the results obtained in part I, analytically closed expressions are derived for the rotational energy levels of ⁴ Sigma states taking into account the changes of the internuclear distances by the centrifugal distortions and the spin forces. The new expressions are applied to the ⁴ Sigma states of the SnH and GeH molecules, and show much better agreement with the experimental data than the earlier formulae, including those obtained in I.

The line broadening theories of Smith et al., Voslamber and Bezzerides are discussed. These theories are related, and then it is shown that all of them depend on the same approximations. The unified theory is then compared to the first order contribution from an expansion formulated by Dufty, and a discussion of the unification is presented.

A phase shift analysis of electron-neon and electron-argon scattering has been made in the elastic region. For neon, a set of s, p and d wave phase shifts consistent with the experimental data and continuous in energy is derived. The predicted phase shifts are in good agreement with theoretical values, except for the p wave, which is significantly smaller. The scattering length is found to be 0.22 a₀. No consistent fit was obtained for electron-argon scattering, and within the model considered, it is suggested that the differential cross section data are inconsistent with that on total elastic and diffusion cross sections. The derived phase shifts (l=0, 1, 2, 3) agree moderately well with theoretical values, except for l=2, where the derived values are substantially smaller. The scattering length is found to be -1.65 a₀, in good agreement with other determinations.

The quantum theory of the integrated absorption coefficient for the collision-induced far infrared rotation-translation spectrum of spherical top molecules is developed. The most general multipolar induction mechanism is considered. A spectral moment is also discussed. Applications are given for the molecules CH₄, CD₄, CF₄ and SF₆.

Earlier work on cross sections for the removal by electron and proton impact of a 2p or 3p electron from all neutral atomic systems in the sequences boron to neon and aluminium to argon is corrected. The new results are in much better agreement with experiment and the work has now been extended to obtain cross sections for certain isoelectronic positive ions.

A study has been made of electron scattering from CO in the energy region 9.5 to 11.5 eV. This has been done at various angles of scattering and in two exit channels which are the v=0 and v=1 vibrational levels of the ground state of CO. In particular a resonance has been studied which we observe at 10.02 eV+or-0.03 eV and with a natural width of 0.045 eV+or-0.005 eV. Other features have also been observed in both exit channels and those in the inelastic channel appear to be due to further resonant processes.

A crossed beam technique has been used to determine secondary electron emission coefficients for He(2¹S), He(2³S), Ne(³P_0.2) and Ar(³P_0.2) metastable atoms incident with thermal energy on atomically clean cadmium and contaminated stainless steel surfaces. The secondary emission coefficients for the atomically clean surface were in all cases found to be less than 0.5, but for the contaminated surfaces values in excess of 0.5 were measured. Mechanisms are suggested to account for the observed large values.

For pt. I see ibid., vol.4, 1683 (1971). Secondary electron emission coefficients for thermal energy He(2¹S), He(2³S), Ne(³P_0.2) and Ar(³P_0.2) metastable atoms incident on a gold surface have been measured using an improved gas cell absorption method. The coefficients for the same metastable species incident on chemically cleaned stainless steel and copper surfaces and on atomically clean cadmium and tungsten surfaces have been determined by calibration against the gold surface. The results indicate that rather larger coefficients than those used hitherto should be used for gold surfaces. The implications of the results presented for the measurement of metastable fluxes are examined.

Measurements of rate coefficients for the charge exchange collision processes Ar⁺N₂, Ar⁺CO, Ar⁺O₂, Ar⁺NO, N⁺O₂, have been made in the energy range 0.04-2 eV in the injected ion drift tube. A new solution procedure for the diffusion problem is presented. Data are sensitive to secondary reactions caused by ions produced in the thermalization of the injected ions; systematic studies of suitable buffer gases habe been made to avoid errors arising from these reactions. Calculations habe been made of cross section functions for charge exchange and ion atom interchange processes using the 'nearest resonance' approximation, including allowance for the exchange interaction, and with restrictions placed upon the rotational quantum numbers of the molecular ion product.

Electron-ion recombination rates (T approximately=300 K) have been measured in a flowing afterglow tube, using an axially traversable ion sampling mass spectrometer and floating double probe. The values are O₂⁺:1.9+or-0.5*10^-7 cm³ s^-1, N₂⁺:2.2+or-0.4*10^-7 cm³ s^-1, NO⁺:3.4+or-0.6*10^-7 cm³ s^-1, and CO₂⁺:3.4+or-1.2*10^-7 cm³ s^-1.

A strongly oscillating beam maser has been used to obtain 2 pi pulse excitation of the molecular beam as a whole. It is shown that when fast molecules in the molecular beam undergo pi pulse excitation, some slow molecules in the velocity distribution of the molecular beam undergo 2 pi pulse excitation, and burn a narrow dip or hole in the wider spectral profile of fast molecules. The phenomenon may be generalized to other molecular beam systems, including a thermal beam.

Equilibrium charge distributions of C⁺, O⁺, N⁺, and Ne⁺ beams in carbon foil have been measured for incident energies of 1 to 5 MeV. There is consistent agreement with previous work in those regions where there are data in common. Charge state equilibrium is reached in foils at least as thin as 6 mu g cm^-2.

A low inductance vacuum spark has been used to produce and excite ions of elements from chromium through copper. The line emission from these ions between 8 AA and 18 AA has been analysed with a bent crystal spectrograph used in the defocused de Broglie configuration. Numerous new emission lines have been recorded and their wavelengths measured. Most of these new features are identified as transitions in ions isoelectronic with Ne I, F I, and O I.

Absolute absorption measurements were obtained for five bands (v"=0, v'=0-4) of the beta (B² Pi -X² Pi ) system of nitric oxide. The absorption bands were investigated using the third order of a 21ft spectrograph (reciprocal dispersion approximately 0.4 AA MM^-1) and instrumental effects were eliminated by argon broadening the absorption lines. The band absorption oscillator strengths range from f_(0.0)^abs=2.46*10^-8 to f_(4.0)^1bs=1.16*10^-5.

Absolute absorption measurements were obtained for eight bands (v"=0, v'=4-11) of the (forbidden) Herzberg I (A³ Sigma _u⁺-X³ Sigma _g^-) system of molecular oxygen. The spectra were recorded at very high dispersion (reciprocal dispersion 0.6 AA mm^-1) and instrumental effects were eliminated by self-broadening the absorption lines. The individual band measurements yield an electronic oscillator strength f_el^abs (Herzberg I) approximately 10^-7.

For pt I see ibid., vol. 4, 1778 (1971). Sensitive photoelectric detection techniques and a ling absorption cell ( approximately 109 ft) were used to obtain cross section estimates of the weak photodissociation continuum adjoining the Herzberg I (A³ Sigma _u⁺-X³ Sigma _g^-) system of molecular oxygen. The measurements cover the spectral region 2430-1920 AA and the cross sections vary from approximately 0.5*10^-24 cm² at 2400 AA to approximately 30*10^-24 cm² at 1920 AA.

Isotope shifts have been measured in the resonance lines of Cd II and SnIV using a diffraction grating and hollow cathode light sources. The following results were obtained. ¹¹⁶Cd, ¹¹⁰Cd; lambda 2144 AA (5s²S₁2/-5p²P₃2/), -70+or-10 mK, and lambda 2265 AA(5s²S₁2/- 5p²P₁2/), -66+or-5mK. ¹²⁴Sn, ¹¹⁶Sn; lambda 1314 AA(5s²S₁2/-5p²P₃2/), -215+or-40 mK, and lambda 1437 AA(5s²S₁2/-5p²P₁2/), -134+or-9 mK. All shifts were in the opposite direction to the normal mass shift (NMS). Isotope-shift data for many alkali-like resonance lines are tabulated and discussed, and it is assumed that for these lines the specific mass shift is NMS+or-NMS. On this assumption the isotope-shift constants were estimated to be 116+or-14 mK for ¹¹⁶Cd, ¹¹⁰Cd, and 130+or-18 mK for ¹²⁴Sn. ¹¹⁶Sn.