Absolute cross sections for near-threshold electron-impact excitation of the 3s21S→3s3p1P and 3s21S→3s3p3P transitions in Si2+

Absolute total cross sections for electron-impact excitation of the ${3s}^{2}{}^{1}S\ensuremath{\rightarrow}3s3p{}^{3}P$ and ${3s}^{2}{}^{1}S\ensuremath{\rightarrow}3s3p{}^{1}P$ transitions in ${\mathrm{Si}}^{2+}$ were measured using the merged electron-ion beams energy-loss technique. The results are compared to $R$-matrix close-coupling theory, which predicts a strong resonance enhancement of the cross section near the threshold for excitation of the ${}^{3}P$ state and this is confirmed by the experiments. The observed disagreement between theory and experiment for the dipole excitation is suggested to be due to resonance interference.