Absolute partial cross sections for electron-impact ionization of SO₂ from threshold to 1000 eV

B. G. Lindsay, H. C. Straub, K. A. Smith, and R. F. Stebbings

J. Geophys. Res., 101, 21,151-21,156 (1996)

Absolute partial cross sections for the production of SO₂⁺, SO⁺, (S⁺ + O₂⁺ + SO₂²⁺), O⁺, and SO²⁺ from electron impact ionization of SO₂ are reported for electron energies from threshold to 1000 eV. The product ions are analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector, making it possible to demonstrate complete collection of all product ions. The overall uncertainty in the absolute cross section values is ±3.5% for SO₂⁺ ions and is slightly higher for fragment and multiply charged ions. While much of the previously published data are in reasonable agreement with the data presented here, the present O⁺ cross section is higher than earlier measurements by approximately a factor of 3. The cross section for production of SO²⁺ has not been previously reported. The sum of the partial cross sections is compared to previously measured total cross sections.