Absolute emission cross sections for electron-impact excitation of the 3p-3s transition in Al2+ -: art. no. 032706

Crossed beams of electrons and Al2+ ions combined with fluorescence detection were used to measure the absolute cross section for electron-impact excitation of the ions to yield 186.3 nm and 185.5 nm photons from the 3s-3p transition. The measured cross section near the 6.7 eV threshold energy is about 16x10(-16) cm(2), and some resonance structure near threshold is indicated. Total relative uncertainties (1sigma) are typically about 6%, to be combined with an 11% absolute calibration uncertainty. Total uncertainties at high confidence level (90%) are around 20%, using a coverage factor of 1.7. Comparisons made with various theoretical calculations, specifically distorted wave and nine-state close coupling, show better agreement of experimental values with distorted wave calculations, with the measured values being higher near threshold than the most recent close-coupling calculations.