We have measured the absolute cross section for electron-impact excitation (EIE) of [Formula Presented] from energies below threshold to 11 eV above. A beams modulation technique with inclined electron and ion beams was used. Radiation at 120.7 nm from the excited ions was detected using an absolutely calibrated optical system. The fractional population of the [Formula Presented] metastable state in the incident ion beam was determined to be [Formula Presented] [Formula Presented] The data have been corrected for contributions to the signal from radiative decay following excitation from the metastable state to [Formula Presented] and [Formula Presented] and excitation from the ground state to levels above the [Formula Presented] level. The experimental [Formula Presented] energy spread allowed us to resolve complex resonance structure throughout the studied energy range. At the reported [Formula Presented] total experimental uncertainty level [Formula Presented] the measured structure and absolute scale of the cross section are in good agreement with 12-state close-coupling R-matrix calculations.
|Number of pages
|Physical Review A - Atomic, Molecular, and Optical Physics
|Published - 1999