Absolute cross section for Si2+(3s3p 3p0→3s3p 1p0) electron-impact excitation

Abstract

We have measured the absolute energy-averaged cross section for electron-impact excitation of Si 2 + (3s3p 3 P 0 →3s3p 1 P 0 ) from energies below threshold to the turn-on of the 3s3p 3 P 0 →3p 2 3 P transition. A beams modulation technique with inclined electron and ion beams was used. Radiation at 120.65 nm from the decay of the excited ions to the 3s 2 1 S ground state was detected using an absolutely calibrated optical system. The fractional population of metastable Si 2 + (3s3p 3 P 0 ) in the incident ion beam was determined to be 0.256′0.035(1.65σ). The experimental energy spread ranged from 0.85 eV (full width at half maximum) at the lowest energies to 0.56 eV at the highest. Resonance features consistent with 12-state close-coupling R-matrix calculations are seen.