Electron-capture and ionization cross sections for collisions ofHe2+with Li: Production ofHe+(3l)at low velocities

Abstract

Single electron capture and ionization cross sections have been calculated for collisions of He(++) with Li over the relative collision velocity range 0.1-10.0 x 10 to the 8th power cm/sec. For low collision velocities (i.e., v = 0.1-0.6 x 10 to the 8th power cm/sec), a molecular approach has been used to determine the electron capture cross section. Ab initio potential energy curves and coupling matrix elements have been computed for the (HeLi)++ system and used in a cross section evaluation based on the perturbed-stationary-state method. For the low velocities, the electron capture reaction He(++) + Li yields He+(3l) + Li(+) is found to dominate the collision process and proceeds with a large cross section, sigma approximately 10 to the minus 15th power sq cm, thus providing the possibility for population inversion and the subsequent emission of Lyman-alpha (304 A) and Lyman-beta (256 A) soft x-ray photons. At the higher velocities (i.e., v=1.4-10.0 x 10 to the 8th power cm/sec), a classical-trajectory Monte-Carlo method has been used to estimate both the electron capture and ionization cross sections. At 2.2 x 10 to the 8th power cm/sec, both cross sections are found to be equal, while one ionization dominates the collisionmore » process at higher velocities and electron capture dominates at lower velocities.« less