Absolute cross sections for near-threshold electron-impact excitation of the dipole-allowed transitions [Formula Presented] in [Formula Presented] and [Formula Presented] in [Formula Presented]

Experimental and theoretical cross sections for electron-impact excitation of the dipole-allowed transitions [Formula Presented] in [Formula Presented] and [Formula Presented] in [Formula Presented] near the excitation thresholds are reported. Absolute cross sections are measured using the merged electron-ion beams energy-loss technique. The intermediate-coupling frame-transformation R-matrix method is used to obtain theoretical cross sections. The total cross sections, for the transitions studied in both ions, exhibit resonance structures near threshold. There is excellent agreement between theory and experiment with respect to both the shape and the magnitude of the cross section for the [Formula Presented] transition in [Formula Presented] For [Formula Presented] structures and trends in both the present R-matrix calculation and the previous calculation of Baluja and Mohan [J. Phys. B 20, 831 (1987)] agree well with the experimental results. However, the magnitudes of the theoretical cross sections for [Formula Presented] are significantly smaller than the measured cross section, which has been corrected for metastable contamination.