Merged-beam measurements of absolute cross sections for electron-impact excitation of S{sup 4+} (3s{sup 2} {sup 1}S{yields}3s3p {sup 1}P) and S{sup 5+} (3s {sup 2}S{yields}3p {sup 2}P)

Absolute cross sections for electron-impact excitation of the dipole-allowed transitions S{sup 4+} (3s{sup 2} {sup 1}S{yields}3s3p {sup 1}P) and S{sup 5+} (3s {sup 2}S{yields}3p {sup 2}P) were measured near threshold using the merged electron-ion beams energy-loss technique. Although the magnitudes of the measured cross sections are in reasonable agreement with available theoretical data, the experimental data indicate that the contributions of dielectronic resonances in the near-threshold region are underestimated by these calculations.