Excitation Mechanisms in Moderate-Energy Na+–He and K+–He Collisions

Abstract

Excitation mechanisms in Na + –He and K + –He collisions were studied at laboratory collision energies of 1000 ¯ Elab ¯ 1500eV by differential scattering spectroscopy. Extensive measurements were performed at Elab = 1500eV. Double differential cross sections ·(©)k were measured over a wide range of center-of-mass scattering angles, 7.3 ¯ © ¯ 173°, by detecting all the scattered particles (Na + , Na, K + ,K , He + , and He), where the subscript k denotes the number of exit channels in the reactions. At the collision energy of Elab = 1500eV, one- and two-electron excitations were observed appreciably for the Na + –He collisions, while only one-electron excitations were observed in the K + –He collisions. The analyses of the experimental results for these collision systems indicate that the electronic transitions in the Na + –He and K + –He collisions take place at the internuclear distances of R 49eV] and R 36eV], respectively. For these asymmetric systems, at Elab= 1500eV, the electronic transition probabilities around the threshold angles are so small that the integral excitation cross sections have small values of Sex < 1.2 © 10 ¹21 m 2 .