Absolute cross section forSi2+(3s3p3Po→3s3p1Po)electron-impact excitation

Abstract

We have measured the absolute energy-averaged cross section for electron-impact excitation of Si{sup 2+}(3s3p {sup 3}P{sup o}{yields}3s3p {sup 1}P{sup o}) from energies below threshold to the turn-on of the 3s3p {sup 3}P{sup o}{yields}3p{sup 2} {sup 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{sup 2} {sup 1}S ground state was detected using an absolutely calibrated optical system. The fractional population of metastable Si{sup 2+}(3s3p {sup 3}P{sup o}) in the incident ion beam was determined to be 0.256{+-}0.035(1.65{sigma}). 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.