REMARKS ON TOTAL AND ELASTIC CROSS-SECTIONS FOR ELECTRON AND POSITRONSCATTERING FROM CO2

There remain discrepancies in the determination of the total and elast ic cross sections for electron and positron collisions with carbon dio xide at impact energies from 0.3 to 100 eV. We have carried out a join t experimental and theoretical study in an attempt to resolve the diff erences. Our measurements for total cross sections for electron impact agree extremely well with those of Hoffman et al. [Phys. Rev. A 25, 1 393 (1982)] above 2 eV, while those for positron impact agree to bette r than 15% in magnitude, and are in an excellent accord for the energy -dependence. The present observations, along with an analysis using a knowledge of the dominant inelastic processes, lead us to conclude tha t the total cross section determined in earlier studies is a considera ble underestimate at intermediate energies, where inelastic processes are not negligible. The analysis provides a rationale for understandin g the discrepancies. Furthermore, we present that the total cross sect ion by positron impact below 2 eV becomes larger by 20% than that of e lectron impact, and provide a rationale as well as implication to a po ssible application. (C) 1997 American Institute of Physics. [S0021-960 6(97)01841-2].