In-plane polarisation correlation study of the 31 D state of helium excited by 40 eV electrons

Electron impact excitation of the 3 1 D state of helium has been studied using the scattered electron-polarized photon correlation method. Results are presented at incident electron energies of 26.5, 29.6, 40.0, 45.0 and 60.0 eV for scattering angles up to 40 • . The data presented here complement the previous large angle data from this laboratory and taken together provide a complete mapping of the dimensionless parameters characterizing excitation of the 3 1 D state of helium over a wide range of both angle and energy. Strong variations in the parameters as a function of energy and angle are discussed. Good agreement is observed between the experimental data and recent theoretical predictions.

Section: Resultssupporting

confidence: 64%

Electron impact excitation of the 3¹D state of helium - an electron-photon coherence study at small scattering angles

Cvejanović¹,

McLaughlin²,

Crowe³

2000

“…On the other hand, it also became clear that the first-order methods were generally unable to reproduce the experimental data for optically forbidden transitions, particularly (1s 2 ) 1 S → (1s3d) 1,3 D ( Bartschat and Madison 1988). A striking example is the circular polarization P 3 of light emitted perpendicular to the scattering plane in the transition (1s3d) 1 D → (1s2p) 1 P o , observed in coincidence with the scattered electron after excitation from the ground state by 40 eV incident electrons (see, for example, McLaughlin et al 1994a). Whereas this energy was too high for the standard R-matrix approach, the CCC method was once again able to reproduce the experimental results very well (Fursa and Bray 1995), thereby indicating the importance of accounting for coupled-channel effects to higher excited discrete and even continuum target states, especially in the 'intermediate energy regime' from the ionization threshold to a few times this energy.…”

mentioning

confidence: 99%

Electron-impact coherence parameters for the 3¹D and 3³D states of helium

Bartschat

1999

Electron-impact excitation of the 3 1D and 3 3D states in helium has been studied using the R-matrix with pseudo-states (RMPS) method. For incident electron energies of 26.5, 29.5 and 40.0 eV, very good agreement is obtained with experimental data for the Stokes parameters measured in electron-photon coincidence experiments, and also with convergent close-coupling (CCC) results. Furthermore, examples of the charge cloud representing the excited state are shown.

“…For D states, maximum information from the electron-polarized photon method is only obtained if a linear polarization measurement is also carried out in the scattering plane. 3 1 D data of this type have been reported by Crowe (1990), Batelaan et al (1991), Mikosza et al (1994), McLaughlin et al (1994a, b) and Donnelly et al (1994). On the other hand, the only complete set of polarization correlation data for the 3 3 D state is that of Crowe et al (1994) for an incident electron energy of 40 eV.…”

Section: Introductionmentioning

confidence: 89%

Electron impact excitation of the 3D states of helium: comparison between experiment and theory at 30 eV

Fursa

Bray

Donnelly

et al. 1997

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 .