Electron impact excitation of the 31D state of helium is studied using the electron-photon polarization correlation technique. Four Stokes parameters are determined at an incident electron energy of 29.6 eV and for scattering angles in the range 40-120 degrees . The data are interpreted in terms of the shape and dynamics of the excited state produced over the range of kinematically defined collisions. The lack of a theoretical model to adequately describe low-energy D state excitation is exposed.
Excitation of the 3'D state of helium by electron impact has been studied by measurement of the linear and circular polarisation of the decay radiation emitted perpendicular to the scattering plane in a polarisation correlation experiment. Results are presented over the angular range 40-120" at an incident electron energy of 40eV. Recent data in the angular range 31.2-50" by Beijers et a1 are confirmed but recent calculations do not agree well with experiment.
A polarisation correlation technique has been used to study electron impact excitation of the 3'P state of helium. Values of the three relative Stokes parameters E',, Pz and P3 are reported over an angular range of 35" to 120" and at energies of 29.6 and 26.5 eV. The data are compared with recent angular correlation measurements from this laboratory and with the predictions of a 19-state R-matrix calculation.
Experimental and theoretical values of the Stokes parameters P 1 , P 2 , P 3 , P 4 are reported for electron impact excitation of the 3 3 D state of helium at 30 eV. The theoretical results are from a 111-state convergent close-coupling (CCC) method. Excellent agreement is obtained between theory and experiment for the Stokes parameters and for the derived parameters describing the shape and dynamics of the excited state. By considering the excitation as the incoherent sum of two coherent processes, an ambiguity in constructing the excited state from the experimental dipole radiation pattern is removed. This provides an attractive way of providing a complete description of the excitation compared with a triple coincidence experiment involving the scattered electron and photons from the 3D-2P-1S transitions. This analysis is also carried out for the 3 1 D state at 30 eV and comparison is made between 111-state CCC calculations and the experimental data of Donnelly et al .
An electron-photon angular correlation technique is employed to obtain excitation parameters for the 33P state of helium. A measurement is reported at an incident electron energy of 39.7 eV and compared with a recent measurement. New data are reported at 29.6 eV over the angular range 40-120" and the measured charge cloud alignment is compared with a recent calculation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.