Electron-photon angular correlations in electron-helium collisions: measurements of complex excitation amplitudes, atomic orientation and alignment

Polarisation and Angular Correlations of Excited P States of Helium and Hydrogen

“…Circular polarisation of the 58·4 nm radiation as a function of the electron scattering angle for an incident electron energy of 81·2 eV in helium, showing the present data at 70° and 108°; Williams (1983) at 10° and 90°; and Khakoo et al (1986). Also shown are experimental values of 7)2 deduced from the angular correlation measurements of Ixl by Eminyan et al (1974); Hollywood et al (1979); Steph and Golden (1980) and Sutcliffe et al (1978); Slevin et al (1980);and Beijers et al (1984). The curve is the theoretical prediction of a distorted-wave theory by Madison and Winters (1983).…”

“…Fano (1957), Macek and Jaecks (1971) and Fano and Macek (1973) showed how angular or polarisation correlation measurements of the scattered electrons and radiated photons, detected in coincidence, could be interpreted in terms of amplitudes and phases, or equivalently state multipoles or elements of a density matrix. Eminyan et al (1974) showed how the measurements could be made for the 21 P state of helium. Subsequently many people, for example, Blum and Kleinpoppen (1979), Herman and Hertel (1982) and Andersen et al (1985), have discussed the coherence of the excited states, the symmetry properties of the scattering process, the angular momentum transfer in the collision and the interpretation of the angular, and polarisation, correlations in terms of the shape and orientation of the electron charge cloud of the excited state.…”

Angular Correlations in Electron?Atom Scattering

“…Extensive measurements of 2 1 p -+ liS angular correlations in helium have been reported (Arriola et al 1975;Tan et al 1977;Ugbabe et al 1977;Sutcliffe et al 1978;Hollywood et al 1979;Williams 1980) and the theoretical predictions have been discussed by Madison and Shelton (1973), Thomas et al (1974), Roberts (1976), Scott and McDowell (1976) and Blum and Jacubowicz (1978). The excellent experiments of Eminyan et al (1973Eminyan et al ( , 1974Eminyan et al ( , 1975 and Standage and Kleinpoppen (1975) established several basic facts about the excitation process for the 21 P -+ 11 Sand 3 1 P -+ 21 S transitions of helium by 80 e V electrons and small scattering angles. The ·emitted light is completely characterized (Born and Wolf 1970) by the Stokes parameters or equivalently by the polarization density matrix, which specifies the polarization P and coherence p. vector properties.…”

Calculation of Electron Impact Cross Sections from Metastable States.

“…In figures 8 and 9 the present predictions of A(2'P) and A(3'p)~~~~u~~J from equation (3) are compared with the measurements of Eminyan at aS (1974Eminyan at aS ( , 1975 and with the availab le distorted wave and many-body calculations. Agreement with experiment is good, particularly at the smaller scattering angles.…”