STATE-RESOLVED COLLISION ENERGY-DEPENDENCE OF PENNING IONIZATION CROSS-SECTIONS FOR N2 AND CO2 BY HE-STAR-23S

The state-resolved collision-energy dependences of Penning ionization cross sections sigma-(E) were measured in an energy range (60 < E < 400 meV) for N2 and CO2 with He*2S3 by using a very high-intensity He* beam (1.8 x 10(15) s-1 sr-1) and detecting energy-analyzed electrons as functions of time-of-flight of He*. The partial ionization cross sections for PI states (N2+:A2-PI-u, CO2+:X2-PI-g, A2-PI-u) were observed to increase more rapidly with the increase of the collision energy than those for SIGMA states (N2+:X2-SIGMA-g+, B2-SIGMA-u+, CO2+:B2-SIGMA-u+, C2-SIGMA-g+). In the studied energy range, the repulsive walls for end-on collisions were indicated to be harder than those for side-on collisions. The directional peculiarity of the potential surfaces was related to the anisotropy in the hybridization of He* orbitals interacting with the target molecules.