Table of contents

An accurate calculation of the elastic electron scattering intensity for H₂(x¹ Sigma _g⁺) in the first Born approximation using the Davidson-Jones wavefunction is reported and compared with intensities based on simpler wavefunctions as well as recent experimental data.

It is argued that photo-electrons emitted from trivalent atoms in a two-photon ionization process are totally polarized if the incident light is of total circular polarization and its wavelength matches the resonance condition for the transition between ground state (n²P₁2/) and the first excited state (n+1)²S₁2/. The estimated photoionization yield compares favourably with that of the analogous process in alkali atoms. Some of the most important conditions for a successful experiment are considered.

The photoionization cross section of Ba I was measured photoelectrically at 237.9 nm. The number density was determined simultaneously by the hook method using the 307.2 nm line. The cross section obtained is (50+or-8)*10^-18 cm², which is a factor of 5 larger than the previously published value based on vapour pressure data.

The lowest six even energy eigenvalues of the three-dimensional quartic oscillator have been calculated by straightforward solution of the secular equation of order 11 using basis functions appropriate to the potential. The corresponding eigenfunctions have been used to calculate matrix elements of r and r², and their convergence suggests that the present solutions are satisfactory representations of the exact solutions.

Ab initio calculations have been carried out on some potential energy curves of the (XeH)⁺ molecule, with particular attention paid to the lowest states. The spin-orbit interaction has been taken into account using a semi-empirical method. These calculations suggest the use of a three-state basis when dealing with H⁺-Xe collisions at low energies. It is also found that the computer MO correlation diagram is in good agreement with that predicted by the 'promotion model' of Barat and Lichten (1972).

The CNDO method has been applied to the system (HCl)_n in order to examine the hydrogen-bonding energy and the effect of charge transfer in solid HCl. It has become apparent that the 3d orbitals of Cl atom will be taken into consideration when the hydrogen bond is discussed.

Satellites to the resonance lines of helium-like ions are distinctive features of the spectra from high-pressure plasmas such as those produced in the absorption layer of a high-intensity laser beam incident on a solid surface. The satellites are spatially coincident with the free-bound continua into the helium-like ions and are produced mainly by dielectronic recombination. Their wavelengths are identified by comparison with Hartree-Fock type calculations. The intensities of some of the dielectronic satellites increase anomalously with the atomic charge of the ion.

The author presents a simple scheme of basis functions piecewise-continuous cubic polynomials, together with a simple quadrature approximation for matrix elements. Applied to the hydrogen atom, the method allows a dozen basis functions to approximate the 14 bound states 1s ... 5f with an average error of 0.03% in energies and 0.2% in the oscillator strengths of the 28 allowed transitions.

It is shown that in the non-orthogonal Hartree-Fock approximation Brillouin's theorem holds for all functions Phi _c* obtained from Phi _c by the replacement of one nl electron by n*l, such a replacement affecting only the radial part of the wavefunction. The orthogonality restrictions of the Hartree-Fock approximation prevent the satisfaction of Brillouin's theorem for some replacements such as nln'lLS to nl²LS. A multi-configuration approximation then exists for which the theorem is valid.

The first two terms in the Z-expansion of matrix elements of the electric dipole transition operator for all 1snl ^1,3L-1sn'l' ^1,3L' transitions in the helium isoelectronic sequence with n,n'<or=4 are calculated. It is demonstrated that an arbitrary screening parameter in a modification of the screening approximation of Dalgarno and Stewart (1960) can be chosen to increase the rate of convergence of the expansion. A practical procedure for choosing the arbitrary screening parameter is presented.

The nuclear-charge expansion method is used to calculate multiplet strengths, correct through first order, for 1s²nl²L-1s²ml'²L' dipole transitions in lithium-like ions for all n,m<or=4. Two distinct procedures, which give results in very close agreement, are used and a modified screening approximation is employed to increase the rate of convergence of the expansions. From these calculated values and experimental energy differences, oscillator strengths and radiative lifetimes for a range of atomic ions are predicted and compared with other available data.

For pt.II, see ibid., vol.6, 1751, (1973). It is shown that a Hartree-Fock calculation of the mean energy of the 2p⁴3p configurations in the F I isoelectronic sequence is able to predict accurately the structure of the configurations with the exception of three terms ((¹D)²P, (³P)²P and (³P)⁴P), for which the deviations correspond to Hartree-Fock wavefunctions appreciably different both from one another and from that obtained for the mean energy. This knowledge is used to improve the parametric fitting of the configurations.

Central field orbitals of several kinds have been employed for the calculation of transition moments and energies for states of the positive titanium ion. Lifetimes have been determined for the different multiplets of the configuration 3d²4p. Limited configuration interaction is included in order to describe the multiplet structure of this and lower lying, even parity, configurations. The results show a fair correlation with the experimental results.

The differential and total cross sections for two-photon detachment of H^- are computed analytically within the asymptotic model for both linearly and circularly polarized light. The total cross section for unit flux is of the order 10^-48 cm². The differential cross section for linearly polarized light is nearly isotropic near the two-photon absorption threshold but is sharply peaked along the polarization direction just below the threshold for one-photon detachment. The circular polarization efficiency is very small near the two-quantum threshold but is close to its theoretical maximum near the one-quantum threshold.

The combined multiconfiguration energy-bound-natural eigenvalue (MCEB-NEV) method has been applied to Feshbach-type ³P^e autoionizing states of H^- pertaining to the n=3 and n=4 thresholds. The lowest-lying state of each cluster has been found to have appreciably positive binding energy compared with that of the (2p²) ³P^e state below the n=2 threshold. The magnitudes of the binding energies are a little smaller than those of the H^-1S^e compound resonant states pertaining to the n=3 and n=4 thresholds.

The authors have parametrized, using Fano's formula, the three resonances associated with the 2s² 1S, 2p²¹D and 2s2p ¹P autoionizing levels of helium. They were observed in energy spectra of ejected electrons produced by proton-helium collisions. For the ¹S resonance, the authors determined the variations with electron emission angle of the shape parameter q and the resonant continuum cross section sigma _r, in the angular range 16.5 degrees to 160 degrees , for 150 keV protons. The dependence on proton energy of these parameters, has also been obtained for 16.5 degrees angle, in the energy range 14 to 150 keV. Additional results concern the variation of the profile parameters for ¹D and ¹P resonances, with ejection angle, at 150 keV.

For pt. I see abstr. A23284 of 1972. A method which has previously been successful in calculating the phase shifts for the scattering of particles by a central potential is applied to the problem of calculating the scattering amplitude directly. Unlike the work of Walters, there is no singularity to be avoided in the integral equation which is approximated by quadrature. The method has been applied to a variety of central potentials and excellent agreement has been obtained with the results obtained by standard phase shift methods. The limitation of the method is that knowledge of the off-shell second Born matrix elements of the potential is required.

Cross sections for transitions among the Na(3p²P_jm) states induced by He(¹S) collisions are calculated for impact energies E<or=0.07 eV by a close coupled wave treatment with an orientation-dependent interaction. The cross section sigma (j'm';jm) for the transition in which the total angular momentum j and its projection m are changed to j' and m', the cross section sigma (j';j) for j to j' transition in which an average over m and a summation over m' are taken, the angular distribution d sigma (j'j mod theta )/d theta , the multipole relaxation cross sections and the polarization transfer cross section sigma _pt are evaluated.

Using the Martin-Schwinger variational technique (1959), a new theory is obtained for electron-atom (molecule) inelastic scattering. This theory constitutes a higher order approximation than the GRPA elastic theory. In analogy with elastic scattering, an equivalent optical potential, named, the transition potential, is introduced for inelastic scattering. In the GRPA this transition potential is of the first-order static-exchange type. The present theory adds three new effects to the GRPA transition potential. One of them represents the screening of the first-order exchange term, another one the transition polarization effect and the third the effect of the final state field. In contrast to close-coupled or Kohn-type variational theories, the present theory has the advantage of decoupling the scattering channels through the use of the energy-dependent transition potential.

The second order transition potential introduced in the previous paper (see ibid., vol. 6, no. 10, 2040 of 1973) is generalized and analysed from the energy-dependency point of view. The adiabatic limit and the first nonadiabatic correction is given. The same potential is analysed also in terms of multipole moments and it is shown how wavefunction methods can be used to calculate it. In the adiabatic, dipole limit the long-range part of the transition polarization potential agrees with the one used in the polarized Born approximation (Truhlar 1970, Rice et al. 1972). The same limit gives a generalization of Temkin's (1957) polarized orbital method for inelastic scattering.

Elastic and inelastic differential measurements in Li⁺-rare gas collisions have been performed in the keV energy range. On the other hand ab initio calculations have been carried out on some potential energy curves of (Li-Ne)⁺ and (Li-Ar)⁺. The experimental data are examined in the framework of the quasi-molecular aspect of atomic collisions leading to a discussion of the validity of the 'electron promotion model' (Fano-Lichten) for outer shell excitation mechanisms.

A new apparatus designed to investigate various aspects of the electron impact dissociative ionization process is described in detail. It is shown that the angular distributions obtained for protons from the ² Sigma _u⁺ state of H₂⁺ are consistent with theoretical arguments and confirm the results of previous measurements. The first angular distribution of protons from the ² Sigma _g⁺ state of H₂⁺ is also reported. Absolute cross sections for the production of protons from both the ² Sigma _g⁺ and ² Sigma _u⁺ state of H₂⁺ at electron energies close to the respective thresholds are also presented. The ratio H⁺/H₂⁺ is measured as a function of incident electron energy for ions originating from the ² Sigma _g⁺ state.

For pt. I see ibid., vol. 6, no. 10, 2088 (1973). The angular distributions of both N⁺ and N⁺⁺ produced in the electron impact dissociation of N₂ are presented for incident electron energies up to 300 eV. The N⁺ distributions show only a small anisotropy and are in excellent agreement with a previous measurement. Angular distributions for the N⁺⁺ ion are also found to show little anisotropy. Absolute ionization efficiency curves for N₂⁺, N⁺ and N⁺⁺ from their respective thresholds to 300 eV are presented and comparisons are made with the results of other workers where available.

A modulated crossed-beam technique has been used to determine cross sections for the four reactions: H⁺+H(1s) to H(2s or 2p)+H⁺ (electron capture) and H⁺+H(1s) to H⁺+H(2s or 2p) (excitation) within the energy range 2.3-26 keV. Results have been based on measurements, using a Doppler-shift identification technique, of the Lyman alpha radiation emitted from the beam intersection region both in the absence and in the presence of an electric field. While cross sections for excitation of the 2s state have not been reported previously, cross sections for capture into the 2s state agree well with those measured by Bayfield (1969a) using a furnace target technique. The H(2p) formation cross sections are also shown to be in reasonable accord with values based on the crossed-beam measurements of Stebbings et al. (1965).

It is suggested that an interaction not being invariant about the internuclear molecular axis is useful for the description of rotational excitation of diatomic molecules in the electronic Pi -state. In the framework of the helicity-basis of angular momentum a complete scattering theory qualified for numerical use is presented. Collision induced excitation by rare gases, Sigma - and Pi -state molecules, are treated separately. Special attention is paid to polarization phenomena. The connection with the usual angular momentum coupling scheme is given explicitly.

The CO₂⁺ ions in the various vibrational levels of the A ² Pi _u electronic state were selectively produced by vacuum ultraviolet radiation of lambda 703, 709, and 715 AA. The emission band strengths of the CO₂⁺(A ² Pi _u to X ² Pi _g) system were obtained and compared with other previous results established by different excitation methods. Good agreement with the earlier work was found. Using existing Franck-Condon factors, the electronic transition moments for the CO₂⁺(A ² Pi _u to X ² Pi _g) bands are also presented.

The natural decay rate of orthopositronium has been measured to an accuracy of 0.20% using a fast counting technique and modified method of analysis. The quenching coefficients for orthopositronium and Z_eff for free positron annihilation in freon, argon, nitrogen and krypton have also been measured.

The spectrum of strontium has been re-examined within the range 2100 AA to 26000 AA. A large number of new lines have been observed and many of these are diffuse. This has led to the identification of new energy levels including the even parity autoionizing levels arising from the 4d5d configuration. A complete list is presented of Sr I and Sr II wavelengths observed within range 7800 AA to 26000 AA together with approximate intensities.

The observation of high-gain amplification by stimulated emission is reported for ten lines in neutral and singly ionized neon in a high current pulsed discharge. The 2.1 mu m (3p₁-2s₂) and 5.4 mu m (3p₁-3s'₁) lines are shown to compete for the population of their common upper level 3p₁. Stimulated emission on the 5.4 mu m transition causes high-gain inversions on two transitions from the 3s'₁ level. The excitation mechanism for the 3p₁ level is suggested to be a stepwise process involving the 1s₂ resonance level.

Absolute absorption coefficients in the region of the M₄ and M₅ edges are presented for cerium in CeF₃, CeO₂ and in the metal. Strong line absorptions (3d to 4f) occur to the low energy side of weak M₄ and M₅ 'edges'. At each 'edge' the absorption passes through a weak broad peak attributed to transitions into a band of higher f states. The spectra of CeF₃ and the metal at room temperature are structurally similar but differ clearly from the quadrivalent oxide. A shift to higher energy is found for both absorption lines and edges in the sequence fluoride-oxide-metal at room temperature. On cooling the evaporated metal absorption foil ( gamma phase) to 77 K both M₄ and M₅ line profiles change into forms accurately resolvable into a combination of trivalent (CeF₃ like) and quadrivalent (CeO₂ like) curves, suitably displaced in energy, in the proportion 59% to 43% respectively.

Decays from highly ionized fluorine atoms obtained by beam-foil techniques are examined in the 670 eV to 1150 eV range. Transitions from the one-electron, two-electron and three-electron configurations are observed. In the H-like and He-like spectra the lines agree well with the known values, and the series limits were observed. The observed Li-like lines are compared with existing calculations and measurements. Two lines, at 800.6 eV and 813.2 eV, are observed but no good agreement is found with any existing calculations.