A quasi-coincidence measurement of the polarization of radiation emitted from the 3 3P state of fast helium atoms populated by He + -He charge transfer collisions

The relative circular polarization of photons emitted in the 2 ³S-3 ³P He I transition near 3889 Å has been measured. The 3 ³P state of fast He atoms was populated by He ⁺-He charge transfer collisions at 3 keV. Radiation from the fast atoms was collected as a function of scattering angle by selecting scattered atoms with an angle defining aperture. Measurement of the relative circular polarization stokes parameter {S}/{I} permitted a direct comparison with theoretical predictions of the magnitude of this parameter. The data appear to be in basic agreement with the predictions of this theory, indicating that the quasi-coincidence or impact parameter selection method can be useful and accurate means to study anisotropic excitation.