Table of contents

The collision strength for the transition C⁺2s²2P²P⁰-2s2p²⁴P is calculated from solutions of coupled integro-differential equations. Configuration interaction between 2s²2p and 2p³ is allowed for in the ²P⁰ ground state. All 2s2p² channels are included. The results have important applications for the interpretation of quasar spectra.

It is shown that differences between the close-coupling calculations of Smith et al. (1969) and of Henry et al. (1969) are due to differences in the adopted phases of fractional parentage coefficients. The phases used by Henry et al. are consistent, but those of Smith et al. are not.

The wavefunctions for neutral carbon are expanded in terms of antisymmetrized products of functions for the C⁺ core multiplied by orbital functions for an added electron. The core functions included are: the ²P⁰ ground state with admixture of the configurations 2s²2p and 2p³; and the states ⁴P, ²D, ²S and ²P belonging to the configuration 2s2p². The radial functions for the added electron satisfy a system of coupled integro-differential equations. Results are obtained for the CI levels normally designated 2s²2p²³P, ¹D and ¹S and 2s³2p3p¹S, ³S, ¹P, ³P, ¹D and ³D.

The transmission without dissociation of MeV H₂⁺ ions through planar directions of a thin gold single crystal is studied. The results indicate that the channelling effects on the transmission yield are very important.

The use of escape factors to compute atomic number densities of optically thick non-thermal plasmas is given a basis of plausibility by examining carefully the validity conditions of Biberman's approximate solution of Holstein-Biberman's integral equation.

Excitation in collisions involving the passage of 70 keV He atoms through thin targets of helium have been studied by a spectroscopic analysis of the spontaneous decay of the 4¹S, 4¹D, 4³S and 4³D excited products of single collisions. A Doppler shift separation of target and projectile emission was possible. The 4³S and 4³D projectile and target emissions are shown to be strongly dependent on the metastable population of the beam.

For pt. I see abstr. A18145 of 1971. A form of the Coulomb T matrix is used in the first order Faddeev-Watson approximation to evaluate e-H elastic differential cross sections at 200 eV incident electron energy. The results confirm the large discrepancy with the Born found by Chen and Sinfailam (to be published) using a similar approximation. Modifications to the form of the T matrix near its energy shell are discussed and it is shown how these can significantly alter the order of magnitude of the differential cross sections.

The key formula of the classical binary encunter approximation is derived from the Born approximation for the differential cross section for a general inelastic collision.

Branching ratios for production of either H(2p) or H(1s) by neutralization of 4 keV protons on He, Ne, Ar and H₂ have been measured by double charge transfer (H⁺ to H^-) translational spectroscopy.

The one electron approximation is used to determine the exact form of the wings of a line broadened by electron-atom collisions. The validity of this model is examined. The profile being proportional to the square of the scalar product of scattered waves, the impact approximation is obtained by replacing the exact form of the scattered waves by their asymptotic form. In this case of hydrogen the quasistatic approximation is obtained by using the JWKB method together with the usual assumptions.

The authors derive a Kohn variational principle for the break-up process of a bound pair of particles colliding with a third particle. Recently Lieber et al. (to be published) have derived such a variational principle avoiding the difficulty that the asymptotic form of the time reversed final state (in which three particles are incident) is not fully known. Their proof involves divergent integrals which they handle by a process which is the analogue for integrals of Cesaro summation. Their derivation also uses the methods of Lieber et al. to overcome the first difficulty but it avoids the need for the Cesaro summation procedure. This is achieved by going from complex to real energies only at a later stage in the derivation than is done by Lieber at el. Their derivation of the variational principle is not rigorous in some respect which are discussed carefully.

Hypervirial theorems are used to derive a differential equation for the transition-moment generating function (A mod exp(itx) mod B) associated with eigenstates A and B in a one dimensional wave- mechanical system. Explicit solution of the equation is possible for the harmonic oscillator, and leads to a simple expression for the overlap integral between two similar oscillators on different centres.

Adiabatic potential energies for the two lowest ¹ Sigma ⁺ states of the hydrogen molecule have been calculated in the frozen core approximation over a range of internuclear separations from 0.2 to 4 au. The results are comparable with the SCF calculation of Coulson (1938) for the X¹ Sigma _g⁺ ground state, and with the multi-configuration calculation of Browne (1969) for the B¹ Sigma _u⁺ excited state. Transition moments for the X¹ Sigma _g⁺-B¹ Sigma _u⁺ electronic transition have also been computed.

A formula previously given (see abstr. A 72212 of 1971) for relativistic atomic energies is used to calculate fine structure splittings in the remaining 1s²2s^asp^b cases. Relativistic corrections to the LS configuration averages are also discussed. The accuracy is comparable to that of the best Hartree-Fock calculations. Some of the results and discussion are relevant to any theoretical method which involves jj configuration averages.

A complete calculation of position-hydrogen elastic scattering in a pseudo-state expansion formulation is made and results obtained for s, p, d, etc., partial wave phase shifts. Good agreement is found between these calculations and those of long range force oriented models for energies below the positronium formation threshold.

Experimental studies of the Li⁺+He interaction have been extended to smaller internuclear separations to clarify a discrepancy between experiment and theory in the elastic cross sections and to observe and measure cross sections for inelastic excitation. For R<or=0.5a₀ the elastic scattering differential cross section is observed to drop far below that expected from a single state interaction based on ab initio ground state potentials. In this same region of R both one and two electron excitations of He are observed to be strongly excited, and cross sections were measured for each of them. The lowest inelastic channel is an electron capture state, which is observed indirectly to be strongly populated also. A diabatic correlation diagram is constructed that exhibits the basic interactions responsible for the excitation.

Elastic and inelastic differential measurements of the Li⁺-He system were undertaken with particular attention given to the charge exchange channels. The energy variation of the 'summed' differential cross sections (elastic, inelastic and change exchange) agrees quite well with the published ab initio ground state calculation, showing that most important channels are considered. All the inelastic and charge exchange processes are discussed in the frame of the diabatic correlation diagram.

Low energy collisions between Li⁺ and He are investigated using a molecular expansion which takes account of rotational coupling between the ¹ Sigma , ¹ Pi and ¹ Delta states of the LiHe⁺ quasi-molecule. Differential cross sections for elastic scattering, and for excitation of those states formed by dissociation of the ¹ Pi and ¹ Delta states, have been computed for incident ion energies of 1.0, 1.5 and 2.0 keV and for a range of scattering angle from 0 to 35 degrees (centre of mass system). The agreement with experiment is satisfactory. It is shown that rotational coupling is an important excitation mechanism in Li⁺-He collisions.

The calculation of cross sections differential in angle and ejection energy for electron production from helium by proton impact is discussed. The existence of a peak in these cross sections for electron velocities close to that of the incident proton is shown to be accurately predicted by the theory when the asymptotic conditions on the final wave-function are established correctly. The ejection of electrons in the direction opposed to that of the protons is linked with the electron correlations in the initial state of the helium atom.

The geometrical aspects of the transfer of polarization are treated in terms of classical tensors: a coherency tensor is used to describe the radiation field and an ensemble polarization tensor is introduced for the system of atoms. Independent of the rotation symmetry of the cell, the evolution equation for the ensemble polarization tensor is found to separate into two parts, the first accounting for the linear polarization properties, and the second accounting for the circular polarization properties. Attention is focused on the latter; the standard result for the decay of orientation is obtained for a spherical cell, and the decay of the orientation for a cell with arbitrary rotation symmetry is found to be characterized in general by three different decay constants.

Widths of JK 0,0 to 0,1 rotational line of the symmetric top molecule CH₃⁸¹Br broadened by polar molecules CH₃Br, OCS and CH₃CN have been measured on a double modulation microwave spectrograph. The experimental data have been compared with the theoretical values as calculated by the Anderson- Tsao-Curnutte theory and Murphy and Boggs' theory taking only dipole-dipole interaction. The theoretical widths obtain from the Anderson-Tsao-Curnutte theory are larger than the experimental values whereas those from Murphy and Boggs theory are somewhat nearer to the measured values.

The authors have measured the alignment destroying collision cross sections for the levels of the 2p⁵ 3p configuration of neon for helium and neon perturbers in a mild discharge at a temperature of 870K. Some of the cross sections, notably those of the 2p₂ and 2p₆ levels, increase rapidly above room temperature and they attribute this to the effect of collisional transfer of excitation to neighbouring levels in the configuration. The relationship between these nonadiabatic cross sections and the cross sections for the collisional relaxation of population reported by other authors is discussed. The authors show that collisional cascade of populations is important for the 2p levels. Most of the other cross sections in the configuration continue to show a weak temperature dependence consistent with an adiabatic collision model with combined repulsive and attractive interatomic potentials.

The variation of the steady state electron mean energy between parallel plates in argon and, for comparison, helium gases has been calculated as a function of the distance from the cathode by a Monte Carlo simulation applying a new technique of sampling steady state localized swarm parameters. A brief preliminary survey for excitation and ionization collision cross sections for argon has been made. The results show that, in both gases, damped oscillatory fluctuations of the electron mean energy follow its initial linear increase from zero energy at the cathode and that a rapid rise above the equilibrium energy occurs in front of the anode. This behaviour has been explained qualitatively in terms of an electron energy balance equation. Position dependent, diffusion modified localized drift velocities are also obtained in connection with the explanation.

Comparisons of experimental and theoretical Stark profiles of the allowed 2¹P-3¹D helium line at 6678AA and of the forbidden 2¹P-3¹P component at 6632AA in a dense plasma were carried out. The plasma was produced by optical breakdown of helium by means of a repetitive, high power CO₂ laser. The allowed line shows good agreement with conventional theory, but discrepancies are found around the centre of the forbidden component. When normally neglected ion motions are taken into consideration, the observed discrepancies are partially removed. Tables of the Stark profiles for the pair of lines are given for electron densities in the range 3*10¹⁵-3*10¹⁷ cm^-3 and temperatures in the range 10000-40000K.

The spectrum of Be III has been studied in the wavelength region 80-6200AA. The energy of the ground state 1s²1S₀ has been determined as 1241253+or-10cm^-1 below the first ionization limit. Members of the ns, np, nd, nf series have been identified as well as one 5g term. About 30 Be III lines are classified and good agreement is obtained with existing theoretical calculations.

The rotational analysis of some bands of the beta band system of the PO molecule has been revised and some new bands, for example (1,2), (3,2), (3,4), (4,3), (4,5) and (7,8) of the subsystem B² Sigma ⁺-x² Pi _3/2 and (4,3), (5,4), (5,5) and (6,7) of the subsystem B² Sigma ⁺-x² Pi _1/2 have been analysed. Perturbation in the 6th and 7th vibrational levels of the upper excited state have been investigated.

Measurements of the lateral diffusion of mass identified O₂⁺ ions in oxygen are reported and comparison made with other available data. Calculations are made of the ratio of the first and second order transport cross sections using the present data and drift velocities obtained by other workers. The conclusion is drawn that the ion-molecule system studied is strongly influenced by spiralling, charge exchange, collisions (due to the polarization attraction of the O₂⁺ ion and oxygen molecule), rather than by 180 degrees scattering collisions, characteristic of long range non-spiralling collisions.

The mobility of mass identified D⁺ ions in helium gas has been measured by the 'four-gauze' electrical shutter method. The low field mobility corrected to 273K is 24.9+or-0.3cm²V^-1s^-1. The helium gas pressure in the mobility tube was in the range 1.85-4.12 Torr, and the deuterium gas concentration was about 0.01%.