Table of contents

Semiclassical solutions of one-dimensional inhomogeneous Schrodinger and Dirac equations are obtained. Using these solutions, the asymptotic behaviour of the Hartree-Fock and Hartree-Fock-Dirac orbitals is found. The asymptotic solution in atom coincides, within an accuracy of a few per cent, with the numerical solution in the region after the classical turning point. Two questions concerning the influence of the exchange interaction are discussed: (i) the change of the long-range behaviour of the wavefunctions and (ii) the violation of the oscillation theorem (additional nodes).

The energy levels of V IV 3d5g were calculated by using both the Hartree-Fock and the semiempirical methods. Although only four experimental levels were assigned to this configuration, it was possible to confirm these assignments and to predict the values of the sixteen missing levels by exploiting the results previously obtained for Ti III and Sc II 3dng (n=5-8).

New data for optically allowed transitions to levels of nsnp(n+1)p (n=4,5 and 6 in Ga, In and Tl respectively) are presented. The structure is analysed by the technique of partial plots and the identifications obtained by Roig (1975) for Al I are thereby carried through to Tl I. The identifications obtained for In I are in substantial agreement with earlier results, but the photoabsorption data reveal that some changes of designation are needed. For Ga I, there is a disagreement between the experimentally based assignments and structure calculations based on scaled Hartree-Fock parameters.

Based on the two-dimensional WKB model, an equation is derived from which the non-relativistic quasi-Landau energy spectrum of hydrogen-like atoms may be easily obtained. In addition, the authors discuss the solution of radial equations in the WKB approximation and its relation with models recently used to fit experimental data.

Lifetimes of 26 atomic levels of titanium I and vanadium I have been determined using selective pulsed laser excitation of the atoms in an atomic beam and applying the delayed coincidence method for registration.

The photoionisation cross section of helium is calculated including the 1s, 2s and 2p eigenstates and 3s, 3p and 3d pseudostates in an expansion of the ¹S^e initial and ¹P⁰ final wavefunctions. Good agreement is obtained with experiment and with other theories when the He⁺ ion is left in its ground state. In addition the position, width and shape of the 2s2p ¹P⁰ autoionisation state is accurately described by the theory. However, while the calculated ratio of the He⁺ ions left in the 2p state to He⁺ ions left in the 2s state is in good agreement with recent experiments of Woodruff and Samson (1982), and is consistent with recent experiments of Bizau et al. (1982) there is a serious disagreement with the many-body theory of Chang (1980) close to threshold.

It is shown that the linear algebraic equations method for evaluating the phase shift from the integral equation for the radial wavefunction describing the scattering of particles, is equivalent to using the Schwinger variational method.

Cross sections for the process Na(3²P₁2/)+ Delta E to or from Na(3²P₃2/) induced by inelastic collisions with ground-state caesium atoms have been measured and the results are discussed with reference to resonant and rare-gas-induced cross sections and non-adiabatic effects.

Simple approximate correction factors for electronic relativistic effects in L-shell ionisation cross sections by low-energy charged-particle impact have been derived. The factors obtained are compared with the relativistic plane-wave Born approximation calculations using the Dirac wavefunctions and with other approximate correction methods. In the energy region of interest, the present method is found to represent well the relativistic effects.

The values of the screening parameter mu ^infinity have been recalculated on the basis of accurate solutions of the Thomas-Fermi equation. The values of mu ^infinity calculated in the present work are larger by 10-20% than the values published in the literature.

Initial results are presented on the elastic scattering of electrons by argon atoms in the neighbourhood of the well known ((3p⁵)_3/2,1/2(4s)²) resonances. An R-matrix calculation is employed to investigate how the resonance characteristics change as the spin-orbit interaction is switched on.

A parameter-free polarisation potential is proposed for the elastic scattering of electrons by polyatomic molecules, based on the method of Pople and Schofield and the work of Temkin. Cross sections are obtained for CH₄ and H₂O using this polarisation potential and a Hara local exchange potential. Agreement with experiment is good.

The absolute triply-differential cross section for K-shell ionisation of silver by 500 keV electron impact was measured as a function of outgoing electron energy. The outgoing electrons were detected in coincidence in a coplanar geometry at scattering angles of -20 degrees and 40 degrees and of -25 degrees and 40 degrees , respectively. The results are compared with calculations of Das and Konar (1974).

For pt.III see ibid., vol.15, no.12, p.1811 (1982). The L₂₃-MM Auger spectrum of argon has been calculated using correlated initial- and final-state wavefunctions based upon a frozen-core model developed previously. The energies and intensities of the ³P satellite lines have been investigated as well as the diagram lines. Strong interactions between (3s3p) and (3p³(²D⁰))nd states, and between (3s²) and (3s3p²(²D))nd states are evident. The effect of these interactions is to shift the diagram line energies downwards by as much as 9.3 eV for the (3s²)¹S line and decrease the diagram line intensities. The intensity lost from the diagram lines appears in intense satellite structure due to the interacting final states. On the basis of the calculations, the assignments of the (3p³(²D⁰))3d³P⁰ and (3p³(²P⁰))3d ³P⁰ optical levels have been interchanged. Some of the final-state satellite doublets have been assigned. Most of the assignments agree with those made earlier by McGuire (1975). From the diagram line intensity calculations it is concluded that interchannel coupling effects are important in redistributing the intensities especially for L₂₃-M₂₃M₂₃ lines. Intensity calculations for final-state 'shake-up', initial-state and spectator satellites indicate that only spectator satellites are of any importance. The total spectator satellite intensities reflect the initial-state population.

The photoabsorption and photoemission of atomic Cr have been obtained in the photon energy range 30 to 70 eV. At the 3p threshold the spectrum is dominated by 3p⁶3d⁵4s(⁷S) to 3p⁵3d⁵4s²(⁷P), 3p⁵3d⁶4s (⁷F,⁷D,⁷P) transitions giving rise to discrete absorption lines and a broad asymmetric absorption band. In contrast to the higher-Z members of the 3d transition metal series the Cr 3p absorption spectrum shows three well developed 3p⁶3d⁵4s to 3p⁵3d⁵4snd Rydberg series converging towards the 3p⁵3d⁵4s⁸P_5/2,7/2,9/2 states of Cr II. The 3d⁴4s⁶D and 3d⁵⁶S photoemission lines are strongly enhanced above the 3p threshold. As a function of photon energy the intensity of the 3d⁵⁶S line shows a symmetric profile, whereas the 3d⁴4s⁶D line is clearly asymmetric thus corroborating the interference between 3p and 3d excitations. Asymmetric profiles are also displayed by the two 3d⁴4p⁶F, 3d⁴5s ⁶D photoemission lines.

Calculations are presented for the degrees of first- and second-order coherence and the spectral distribution of the light emitted in resonance fluorescence by a two-level atom driven by monochromatic incident light. The theory includes the effects of both homogeneous and inhomogeneous broadening, but is restricted to ranges of the parameters for which analytic solutions can be obtained. There is a further restriction to forward scattering in the case where the inhomogeneous broadening is caused by the Doppler effect. The results show marked differences between the effects of the homogeneous and inhomogeneous broadening mechanisms.

A Thomas-Fermi equation for many-electron atoms in magnetic fields of arbitrary strength is derived. The equation determines self-consistently both the electron number density with spins parallel and that with spins antiparallel to the external magnetic fields, and describes the process of spin rearrangement of the ground state of atoms. By an appropriate scale change, the equation reduces to a universal form independent of the atomic number for neutral atoms. Numerical results are also shown for the total energy, the total spin, the atomic radius and so on as a function of the magnetic field strength.

A resonance interaction of two autoionising atomic states with an external electromagnetic field is considered. The dispersion curve for absorption of the second weak (probe) wave is found. Conditions are found for which the narrower of the two peaks of this curve has a minimum width. The widths of the peaks are found analytically. The possibilities of narrowing are discussed.

A strong radio-frequency field couples two excited atomic states which also interact with the virtual radiation field. The radio-frequency field dresses the atomic states and the virtual radiation field causes them to decay spontaneously. The spectrum of the emitted radiation is calculated by Fourier transforming the differential equations for the amplitudes. The solutions are given in terms of recurrence relationships which can be evaluated to any desired accuracy. The optical radiation field acts as a probe on the dressed atomic states. The spectrum shows all the radio-frequency induced resonances. The frequencies of the states and the Bloch-Siegert shifts of the multi-photon resonances can be deduced from this spectrum.

The broadening and shift induced by helium and argon in the singlet neutral resonance line and the resonance doublet of the first ionised stage of magnesium, calcium and strontium are reported. The pressure-broadened components were extracted from predominantly Gaussian profiles by full numerical analysis and the resulting cross sections are discussed in the context of other data for these transitions.

Reports the optogalvanic detection of observables induced by optical pumping in metastable states of neon. As with optical methods signals are obtained which are related to electronic and nuclear orientation or alignment. Many optical pumping experiments may thus be performed using optogalvanic techniques, including the Hanle effect and 'velocity selective optical pumping' described. Different mechanisms are discussed from which optogalvanic signals related to non-scalar observables may originate. Profiles obtained from frequency sweeps of two polarisation-modulated counterpropagating pump beams indicate the dominant mechanism is a second-order pumping effect which induces a modulated depletion of the metastable state. No effect has been observed arising from a variation of the Penning collision cross section when the two metastable colliding atoms are oriented. The analogy between signals produced by optogalvanic and optical methods are pointed out.

Using two CW dye lasers barium Rydberg states were populated by stepwise two-photon absorption via the 6s6p ¹P₁ intermediate level. Monitoring the transmission of the first laser beam, tuned to the resonance line, and scanning the second laser across the upper atomic transition, a greatly enhanced signal was observed. Taking optical pumping into account, a simple rate equation model can quantitatively describe the increase in sensitivity. This technique was applied to measure the hyperfine structure of the 6s15d ¹D₂ Rydberg state in barium.

The author presents a theory of resonant multiphoton ionisation by multimode laser light. He investigates N photon resonant N+1 photon ionisation for a high order bound-bound transition with the resonance dominated by the Stark shift. Two aspects of the problem are considered. He studies the bandwidth dependence for the resonant ionisation probability, approximating the multimode laser light by a chaotic field. Secondly, he investigates the effects of finite mode numbers of the multimode laser. Finally, the theory is compared with the recent experimental results of Lompre et al (1981).

The VUV luminescence spectra of argon excited by alpha particles at a few hundred Torr present two continua, at 180 and 127 nm. The 127 nm emission is very intense, it corresponds to transitions from the lowest vibrational levels of the A 1_y(³ Sigma _u⁺) and B O_u⁺(¹ Sigma _u⁺) states of Ar₂ towards the dissociative X O_g⁺(¹ Sigma _g⁺) ground state. The shape of the pulse corresponding to the emission of the second continuum was reconstituted by time amplitude conversion. Three exponential terms can be seen. The variation of the time constants with pressure allows a kinetic scheme for the formation and decay of the radiative molecule species to be established. The excited states of the argon molecule are created by three-body collisions, from the (1)()J=1 and (1)()J=2 states of the 3p⁵4s configuration, the collision constants being 1.6 and 13.8 Torr^-2 s^-1 respectively. The radiative lifetime of the A 1_u(³ Sigma _u⁺) state is 2.86 mu s.

For pt.I see ibid., vol.15, p.2935 (1982). Spectroscopic and kinetic study of ultraviolet emissions from argon-xenon mixtures brings to light very large energy transfers from argon and xenon. When small amounts of xenon (a few ppm) are added to argon, the argon continua disappear and simultaneously Xe resonance lines can be seen. At higher Xe concentrations (of the order of a few per cent), the spectra of mixtures are similar to those obtained in pure xenon. Kinetic analysis of the main VUV emissions of the two gases allows a complete kinetic scheme of the transfer phenomena to be established. Excited radiative xenon states are created from Ar₂* molecules and atomic precursor states. The ¹P₁ state of xenon is excited by two-body collisions with the excimer Ar₂*(³ Sigma _u⁺) which is responsible for the second argon continuum (k=1.5*10⁷ Torr^-1 s^-1). The transfer is also observed from the Ar*(³P₁) state towards highly excited xenon levels (configuration 5f) (k=2.4*10⁷ Torr^-1 s^-1). Both these paths lead, directly or indirectly, to the production of the ³P₁ and ³P₂ states of xenon which, through three-body heteronuclear collisions, are involved in the formation of the radiative Xe₂* states responsible for the emission of the second continuum at 173 nm. The lifetime of this state, tau =106 ns, is not modified by the presence of argon.

Differential cross sections for elastic and excitation transfer scattering were measured for He(2¹S)+Ne collisions at kinetic energies between 25 and 225 meV. A kinematic analysis and time-of-flight measurements show that Ne atoms can be excited into all energetically allowed states. From simultaneous fits of the elastic and inelastic differential cross sections information is obtained on the interaction potentials and the energy transfer cross sections. Total cross sections are in agreement with measurements in He-Ne discharges. The threshold for the pumping process of the 6328 AA line of the He-Ne laser, He(2¹S)+Ne to He+Ne(2p⁵5_s¹P₁), is higher than previously assumed. The potential curves derived offer a simple explanation of the large differences in the cross sections for He(2¹S)+Ne to He+Ne(2p⁵5s¹P₁ and ³P_0,1,2), which is inconsistent with the commonly accepted Wigner spin rule.

Model potential calculations of Dolan and Masnou-Seeuws (1981) have predicted that rare-gas collisions could induce a population transfer from a Rydberg (n+1)p level to the nl (1>or=2) manifold. Such transitions would not be predicted by the Fermi model. A time-resolved laser fluorescence experiment has been performed. A selective population transfer from Na 6p to Na 5l (l>or=2) due to He Ne, Ar perturbers was observed, the time constant being a linear function of pressure. A comparison is given with theory in the framework of a two-step collision model. The experimental cross sections are then 26, 9.7 and 37 AA² for He, Ne and Ar perturbers, while the theoretical cross sections are 19, 20 and 6.5 AA² respectively.

A semiclassical model is presented for fine-structure transitions of alkali atoms induced by collisions with diatomic molecules. The model illustrates an essential difference that arises when the collision partner is a molecule instead of a rare gas, an additional region of non-adiabatic coupling (curve crossing) caused by the anisotropy of the molecule. Calculations have been carried out for collisions of K(4²P₁2/) and Rb(5²P_1.2) with H₂ and N₂ in the energy range E(cm)<or=0.5 eV; the cross sections obtained are in reasonable agreement with recent experiments. The results indicate that the collisions involving H₂ are strongly influenced by the additional curve crossing. The formation of an intermediate ionic complex is also considered. This mechanism appears to dominate the Rb*-N₂ interaction and to play a smaller role in the other systems.

Reports classical trajectory calculations showing that within the sudden approximation, for a wide range of energies and potentials typical of atom or ion-linear molecule interactions, there exists, for each scattering angle, a symmetry axis to which the angular momentum transfer is approximately perpendicular. The author finds that the direction of this axis is well approximated by the bisector of the initial and final directions of the projectile, scattered by the isotropic potential component. The existence of this symmetry axis is a consequence of the short-range forces characterising these collisions and is shown to be less pronounced as the range of the force increases. When near orbiting collisions occur then this symmetry breaks down.

K-shell ionisation cross sections of Cu, Ge, Mo and Ag in ⁴He ion impact have been measured systematically in the energy range 0.8 to 1.8 MeV in steps of 0.1 MeV. Thin targets have been used in transmission geometry. Data are compared with the predictions of the PWBA and the PWBA modified to include corrections due to Coulomb deflection of the projectile, increased binding of the target electron during collision and the relativistic nature of the K-shell electrons. The intensity ratios K_alpha /K_beta have also been obtained as a function of ⁴He ion energy for all the four elements.

The scattering angle dependence of the quasi-molecular K radiation was measured for 90 MeV Ni-Ni collisions by a particle-photon coincidence technique. The measured K molecular orbital (MO) X-ray emission probabilities are in good agreement with the calculated two-collision 1s sigma MO X-ray production probabilities at impact parameters b>or=400 fm. The data clearly demonstrate the necessity of folding the scattering angle dependence of the probability of creating the initial projectile K vacancy with the probability of the MO X-ray emission. At small impact parameters (200<b<500 fm) and high photon energies E_x>25 keV the contribution of the one-collision 1s sigma MO radiation partially exceeds the two-collision contribution.

Cross sections for electron capture by H and D in caesium vapour and for electron loss by H in N₂ have been measured in the energy range 0.1-5 keV. Ions produced by either of these reactions were measured in identical geometric arrangements by means of two Faraday cups with different angular acceptances. The authors found that projectiles are scattered to larger angles in the electron-loss reaction than in the electron-capture reaction. The present results for the capture cross section sigma _0- are in good agreement with recent measurements and with a calculation by Olson (1981).

The eikonal form of the exact impulse approximation to electron capture in heavy-ion collisions has been evaluated. Comparison has been made to the peaked form of the impulse approximation, and the exact and peaked second Born expressions. It is found that there are two prominent features of the differential cross section, which all these approximations reproduce with greater or lesser, success; the Thomas peak at scattering angle square root 3 m/2M (m, electron mass; M, projectile mass), and a minimum in the differential cross section at scattering angle m/2M. The peaked second Born amplitude is further analysed to show that whereas the Thomas peak is classical in origin, the minimum is produced by quantum mechanical interference between the first and second Born amplitudes. Finally the effect of an internuclear Coulomb interaction is considered, and it is shown that though the position of the Thomas peak is shifted by the Coulomb interaction, the peak itself will not be destroyed.

The relativistic second Born approximation is used to derive an approximate analytical expression for the scattering amplitude for electron capture by a nucleus of charge Z_Be, moving with ultrahigh relativistic energy, from a target hydrogenic ion having nuclear charge Z_Ae. By expanding in powers of alpha Z_A and alpha Z_B, where alpha is the fine-structure constant, and retaining the leading terms it is shown that the second-order contribution to the capture cross section falls off as E^-1 at ultrahigh relativistic impact energies E and is not negligible in comparison with the relativistic first-order OBK approximation which also has an E^-1 decay.