Table of contents

The interaction energy between the two arbitrarily oriented anisotropic non-polar molecules represented as dipoles is derived using a new nonperturbative method valid for all separations. The results of London, Casimir and Polder, and Craig and Power emerge as special cases.

The cross section for collisional quenching of metastable deuterium in collisions with molecular hydrogen has been measured for velocities between 0.35*10⁶ and 8*10⁶ cm s^-1 using a time of flight method. Results are compared with theoretical predictions and other experimental work in this velocity range.

The absorption spectrum of BF₃ gas in the K edge region of boron ( approximately=190 eV) has been measured under high resolution using synchrotron radiation. The observed spectra are consistent with an energy level scheme for the excited states of the molecules proposed by Walsh. The onset of K absorption shifts to higher energy on going from boron metal to BCl₃ to BF₃.

The yield of atoms from the break up of H₃⁺ ions in hydrogen gas was measured as a function of target thickness at H₃⁺ energies of 410, 510 and 550 keV. The maximum yield was found to be 0.710, 0.645 and 0.639 atoms per H₃⁺ ion respectively. The use of single particle counting techniques and pulse height analysis enabled the statistical error in the results to be reduced to less than 1%. These results were required for assessing the use of a beam of fast hydrogen atoms as a method for heating plasma to thermonuclear ignition temperatures.

An optical method of detecting electron polarization which measures the polarization at any desired angle to the electron momentum with equal efficiency is proposed. The method requires no calibration and is intermediate in efficiency between low and high energy Mott detection.

Previous observations of broadened lines in high-density laser generated plasmas set limits on plasma polarization shifts at least one order of magnitude smaller than current theoretical predictions. A correction to the theory is suggested which would remove this discrepancy.

The Rayleigh-Ritz variational method utilizing the Sturmian-Legendre basis set has been applied to doubly excited P states of even parity of the He I isoelectronic sequence in order to obtain the nonrelativistic energy positions of the lowest lying states. The states themselves are of physical interest to study since they are metastable against autoionization within the LC coupling approximation. The energy positions are of importance as initial states for electronic transitions now being studied by the beam-foil technique. For helium the wavelengths of possible allowed transitions and the corresponding wavefunctions are given. A comparison of the results with those obtained by other theoretical calculations has also been included.

The effective Z values for hydrogenic wavefunctions for multi-electron atoms, as reported earlier by Tankhiwale and Mande, have been utilized for the calculation of the electrostatic interaction integrals and also for the computation of the spin-orbit matrix elements for the L shells of some atoms. These have then been used to calculate the energies of the K-LL Auger electrons assuming an intermediate coupling between the electron vacancies in the final state. The calculated values of the Auger energies are found to be in fairly good agreement with the experimental values.

The errors in an earlier calculation (abstr. A16475 of 1962) of the third-order Hartree-Fock energy for the 1s2s^1,3S states of helium- like ions are corrected.

The mobility of protons in helium gas has been measured by the 'four-gauze' electrical shutter method. Extrapolation of low field measurements to zero field gave the value of the mobility, corrected to 273 K, as 31.8+or-0.3 cm² V^-1 s^-1. The gas temperature was 300 K. The H⁺ ions were identified with a quadrupole mass spectrometry during mobility measurements. The helium gas pressure in the mobility tube was in the range 1.96-3.54 torr, and the hydrogen gas concentration was about 0.01%. H⁺ ions were produced from the gas mixture by dc glow discharge. The measurement results compared with the value calculated from Langevin's polarization limiting theory showed a deviation of 7%, whereas the figure obtained from Dickinson's quantum mechanical calculations gave a deviation of 4%.

Attempts have been made to represent the viscosity and second virial coefficient of polar gases by using the same set of force parameters for the 12-6-3 potential. For this purpose, the contributions of the nonspherical interactions other than the dipole-dipole term have been considered for the second virial coefficients. The results are worse than those obtained previously for the preaveraged potential for dipole-dipole interaction. The reasons for the superiority of the preaveraged potential over the 12-6-3 model have been discussed.

The rational Pade approximants are proposed to calculate the cross sections for the elastic scattering of electrons by hydrogen and helium atoms. The relation between these approximants and the Schwinger variational principle is used to evaluate the second perturbative order. The contribution from the terms that correspond to the lowest intermediate states is exactly evaluated and that from all the others is replaced by a single state. The energy of this state is determined by requiring the stationarity of the modulus of the forward scattering amplitude. This approach is a high energy approximation. The theoretical results for elastic e-H scattering are reported. For elastic e-He scattering a fair agreement with the available experimental data is obtained at energies greater than 300 eV.

By treating the centrifugal barrier l(l+1)/2r² as part of the physical potential it is shown that partial wave scattering information may be calculated, using the Fredholm method, for arbitrary values of l without using the usual distorted basis of spherical Bessel functions. This is true in spite of the fact that the Fredholm series formally diverges for a potential for which lim_{r to 0} r²V(r) not=0. A general method is outlined which is capable of handling both single and multichannel scattering problems. Examples of its use are given.

The proton-hydrogen ground state charge transfer process is studied in a first order approximation in which the proton-proton interaction is treated as belonging to the unperturbed part of the problem. This results in the appearance of a Coulomb wave rather than a plane wave in the final state of the T matrix. The result is a cross section which lies between the Brinkmann-Kramers and Jackson-Schiff results, with the high energy limit of 0.810 sigma _BK.

For pt. I see ibid., vol.4, no.10, 1288 (1971). The cross sections for the excitation of the 2s, 2p, and 3s states of hydrogen by electron impact are evaluated at high energy in a first order approximation in which the interaction between the incident electron and target proton is represented by a Coulomb wave final state in the T matrix. In the usual Born approximation this interaction has a vanishing contribution because of the orthogonality of the atomic states. The evaluated total cross sections converge to the Born result at high energies, but the differential cross sections at large angles show marked disagreement with the Born approximation and reasonable agreement with experiment. It is concluded that for non-forward inelastic scattering the Born approximation does not converge to the correct result in the high energy limit.

The cross sections for photoionization of He, Li⁺, B³⁺, O⁶⁺, Ne⁸⁺ and Mg¹⁰⁺ are calculated in both the length and velocity formulations using the Hartree-Fock wavefunction for the continuum state and a 20 parameter correlated wavefunction for the ground state. Relativistic effects are not considered. The results are estimated to be accurate to about 1%. It is also shown that the calculated cross sections may be used to derive accurate photoionization cross sections for other ions in the helium isoelectronic sequence and specific results are given for Li⁺, Be²⁺, B³⁺, C⁴⁺, N⁵⁺, O⁶⁺, F⁷⁺, Ne⁸⁺ and Mg¹⁰⁺. The theoretical values for two electron ions are found to be in good agreement with measured K shell photoionization cross sections.

The elastic scattering of electrons by helium atoms and the excitation of helium to the 2¹S and 2¹P states by electron and proton impact are investigated using a simplification of the second Born approximation in which the terms arising from the coupling to the 1¹S, 2¹S and 2¹P states are evaluated exactly and those arising from couplings to all the higher singlet discrete states and continuum states are estimated by employing the closure formula.

An attempt is made to calculate the polarization of the light emitted by diatomic molecules excited by electron impact. The theory of Percival and Seaton is extended to molecules in two simple cases; the united atom approximation and the Born approximation. The effects of the fine ahd hyperfine structures, electron exchange, cascade decay, are expressed. No account is taken of the polarization of the molecule induced by the incident electron.

A technique employing inclined beams of electrons and ions has been developed and used to measure cross sections of the reaction H^-+e to H+2e for interaction energies between threshold (0.75 eV) and 30 eV. the magnitudes of the cross sections agree closely with results which Peart et al. obtained, for energies greater than 12.5 eV, with normally inclined beams. At energies close to 14.2 eV a pronounced structure has been observed in the detachment cross section. This could be attributed to the formation of a state of H^2- with a lifetime of order 10^-15 s.

Simultaneous Stokes and anti-Stokes electronic Raman scattering has been obtained between the resonance doublets of potassium and rubidium atoms selectively excited by a frequency tunable dye laser. New Raman scattering components near the resonance lines have been observed with rubidium in the presence of helium.

Experimental profiles have been obtained at electron densities of the order of 10¹⁶ cm^-3 of the helium II 3023 AA transition, of two isolated He I lines ( lambda lambda 3965 and 2945) and of the important He I lambda 4471 transition and nearby forbidden component. Comparison with theory shows good agreement for the He II and isolated He I lines, but the discrepancy in the profile of He I lambda 4771 near the 2³P-4³F forbidden component can only partly be accounted for by density inhomogeneities in the source.

For pt. I see ibid., vol.4, no.10, 1353 (1971). The He I lambda 4471 2³P-4³D and lambda 4921 2¹P-4³D lines and their associated 2³P-4³F and 2¹P-4¹F forbidden components have been studied in a highly reproducible and homogeneous plasma produced in the after glow of a Z-pinch discharge. Electron densities in the range 3*10¹⁴<n_e<10¹⁵cm^-3 were determined with high accuracy by interferometric and spectroscopic means, and electron temperatures were estimated spectroscopically. Full experimental line profiles for both lines are compared with theory at two electron densities. An important discrepancy between theoretical and experimental values for the forbidden component intensities and shapes, previously reported briefly by the authors for one line and one density, is confirmed for both transitions.

Quantum mechanical calculations have been carried out for the broadening by electron impact of the lines Mg⁺3p-3s at 2802 AA and Ca⁺4p-3d at 8542 AA. The line broadening function is averaged over the resonances in the elastic scattering of the electrons by both the initial and final states of the ion. The results agree well with recent semiclassical calculations for the width but badly with those for the shift. This is due to the omission from the electron scattering calculations of states which contribute to the polarization of either the upper or lower levels of the line. Comparison with experiment is inclusive in view of the uncertainty in the experimental determination of density and the small number of experimental points.

For pt. I see abstr. A25410 of 1971. The usefulness of a 'model building' approach to rare earth configuration interaction is emphasized as an alternative to doing full ab initio calculations. Second order perturbation theory is used to calculate the eleven parameters which characterize the effective two-electron magnetic interaction in both Pr²⁺ and Pr³⁺. Good agreement is obtained with the Pr²⁺ experimental parameters without introducing screening.

The temperature dependence of the ³⁵Cl n.q.r. frequency for both the lines in HgCl₂ has been studied. The results have been interpreted on the basis of Bayer-Kushida and Brown's theories. The lattice frequency has been found to be very much lower than that obtained from Raman spectra data.

Molecular spectra of BaF have been observed in thermal emission from a high temperature vacuum graphite furnace. New bands, mostly involving higher vibrational quanta, have been identified in almost all the known systems of this molecule and the respective vibrational analyses have been confirmed or modified, utilizing the additional data so obtained. A new band system I has also been recorded in the ultraviolet region.

The (0, 0) and (0, 1) bands of the C₁ system ( lambda 2600- lambda 2700 AA) of the SbF molecule have been photographed at a reciprocal dispersion of 0.35 AA mm^-1 on a two metre plane grating spectrograph. The fine structure analysis has been carried out and an electronic transition ³II₁ to ¹ Delta ₂ has been ascribed to the system. The rotational constants of the two isotopic species ¹²¹Sb ¹⁹F and ¹²³Sb ¹⁹F have been determined.