A Crowe

The scattering of electrons from inert gases. II. Absolute differential elastic cross sections for neon, krypton and xenon atoms

For pt.I see ibid., vol.8, no.10, p.1670 (1975). Measurements of the absolute differential cross sections for the elastic scattering of electrons from neon, krypton and xenon for a wide range of electron energies and scattering angles and with high angular resolution are presented. The range of electron energies is 20 to 400 eV, the range of scattering angles from 20 to 150 degrees and the angular resolution of both the incident and scattered electron beams is 1.5 degrees. The experimental method is based on the crossed electron and modulated atom beams techniques. Measured angular distributions have been made absolute by carrying out phase shift analyses over the 19.35 eV (1s2s2)2S resonant state of helium and the 11.10 and 11.27 eV (3s23p54s2), 2P1/2, 2P3/2 resonance doublet in argon coupled with accurate determinations of the beam density ratios of neon, krypton and xenon to helium and argon. The absolute differential cross sections are not consistently in agreement with any previous absolute determinations.

Measurements of angular correlations in electron impact inner-shell ionisation

The first measurements of the angular correlation between a scattered electron which has ejected a bound electron from an inner atomic shell and one of the decay products of the ion formed are presented. Ionisation of the 2p3/2 shell of argon has been studied by measuring the angular correlation between the scattered electron and the L3-M23M23(1S0) Auger electron. The measured angular correlations exhibit considerable anisotropy.

Alignment and orientation of the 21P state of helium by electron impact at 29.6 and 51.2 eV

The electron-photon coincidence technique has been used to deduce the lambda and chi parameters for excitation of the 21P state of helium by electron impact at 29.6 and 51.2 eV incident energies and for electron scattering angles in the range 15 to 130 degrees . The lambda parameter shows a minimum at small and large scattering angles. When combined with the 1979 data of Hollywood and co-workers at 81.2 eV, it can be seen that as the incident energy decreases, the depth of the low-angle minimum decreases and its position moves to larger scattering angles. In contrast, the depth of the second minimum increases with decreasing incident electron energy. The experimental values of lambda and chi are compared with values predicted from the first Born approximation, a distorted-wave polarised-orbital approximation, a first-order many-body theory and an R-matrix theory.

Auger electron lineshapes measured in coincidence with scattered electrons

The value of Auger electron lineshapes measured in coincidence with outgoing scattered electrons following electron impact inner-shell ionisation in free atoms is discussed. Preliminary data of this type are reported for the first time. Measurements for the L2-M2,3M2,3(3P0,1,2) line of argon confirm the feasibility of the technique for the study of post-collision interaction effects in Auger electron decay. The data are compared with the semiclassical calculations of Niehaus (1977) for photoionisation.

Alignment produced in ionisation of the 2p shell of argon by specific moment transfer electron collisions

Measurements of the angular correlation between scattered electrons which have ejected bound electrons from the 2p3/2 shell of argon and L3-M2,3M2,3(1S0) Auger electrons resulting from the decay of the ion are presented. Distortion of the angular correlations due to the detection of correlated electrons from other ionising events is highlighted by corresponding studies for the 2p1/2 shell of argon.

Angular correlation measurements for the electron-excited 31P state of helium

Angular correlations between the scattered electrons resulting from the 11S-31P excitation process in helium and the photons emitted in the decay of the 31P state to the ground state have been measured. Data have been obtained at incident electron energies of 34.6, 45.6 and 75.6 eV for electron scattering angles up to 35 degrees . Analysis of the data gives the ratio of differential cross sections for excitation of the degenerate magnetic sublevels of the state, the magnitude of the phase difference between the corresponding excitation amplitudes and the Fano-Macek orientation and alignment parameters. Reasonable agreement is obtained between the present data at 45.6 and 75.6 eV and the original data of Eminyan et al. (1975) at 50 and 80 eV respectively. Even at these small scattering angles, no theoretical work yields values for these fundamental parameters in agreement with experiment.

Experimental and theoretical studies of the electron impact alignment and orientation of the 21P state of helium below the ionisation threshold

The alignment and orientation of the 21P state of helium by electrons of incident energy 24.0 eV has been studied both experimentally and theoretically. Experimentally, the angular correlation between the 2.8 eV scattered electron which has excited the state and the 58.4 nm photon resulting from its decay has been measured for electron scattering angles up to 120 degrees . Theoretically, the alignment and orientation parameters have been calculated using a five-state R-matrix method. There is excellent agreement between theory and experiment at all scattering angles.

Low-energy electron impact excitation of the 21P state of helium

Angular correlations between scattered electrons which have excited the 21P state of helium from its ground state and the 58.4 nm photons from its subsequent decay have been measured for an incident electron energy of 26.5 eV and for electron scattering angles up to 120 degrees . The variations of both the lambda and chi parameters with electron scattering angle differ significantly from previous measurements at higher incident electron energies. There is good agreement between experiment and the R-matrix calculations of Fon et al. (1980) for lambda over the whole angular range.

Electron-photon angular correlation study of electron impact excitation of the 4p5(2P3/2)5s3P1 state of krypton

Excitation of the 4p5(2P3/2)5s3P1 state of krypton by 30 eV incident electrons has been studied using the electron-photon angular correlation technique. The alignment and orientation of this state can be completely described using four independent parameters, three of which can in principle be obtained from the present measurements of angular correlations with two detector geometries. Difficulties encountered in the extraction of the spin-dependent parameters are discussed. There is generally good agreement between the experimentally measured angular correlations and distorted-wave Born approximation predictions.

Electron impact excitation of the 31P state of helium using the electron-photon angular correlation technique

Excitation of the 31P state of helium by low-energy electrons has been studied by measurement of the angular correlations between the scattered electrons and the 501.6 nm photons emitted in decay to the 21S state. Measurements have been made over a large angular range at incident electron energies of 26.5 and 29.6 eV. Comparisons are made with a very recent 19-state R-matrix calculation and with 21P data previously reported, McAdams et al. (1980), Crowe and Nogueria (1982).