Differential cross sections for electron impact excitation of then= 2 states of helium at intermediate energies (80, 100 and 120 eV) measured across the complete angular scattering range (0–180°)

Differential cross sections (DCS) for inelastic electron scattering to the n = 2 states in helium have been measured at incident energies of 80, 100 and 120 eV. These DCS have been determined across the complete angular scattering range (0–180°) using a magnetic angle changer (MAC) with a soft-iron core. The convergent close-coupling (CCC), R-matrix with pseudostates (RMPS), and B-spline R-matrix (BSR) methods have been used to calculate these DCS. Agreement between the experimental data and the predictions from these highly sophisticated theoretical methods is generally good. The remaining discrepancies mainly occur at small and large angles for the triplet states 2 3 S and 2 3 P, whereas excellent agreement is found between 30° and 150°. The small-angle differences are likely due to contamination of the observed experimental signal from the neighbouring 2 1 S and 2 1 P states. The present results demonstrate the effective use of a soft-iron core MAC for DCS measurements at intermediate energies, extending the operational energy range of such devices by a factor of approximately 25.