Absolute total and one- and two-electron transfer cross sections for $\mathrmAr^\mathitq+$ (8$≤$ q $≤$16) on He and $\mathrmH_2$ at 2.3 q keV

Absolute values for the total and one- and two-electron transfer cross sections for Arq+ ions (8â¤qâ¤16) colliding with helium and molecular hydrogen at 2.3q keV laboratory energy were measured by the growth-rate method. The He and H2 total cross sections as a function of Ar-projectile L-shell occupation number increase monotonically from Ar8+, 2p shell full, to Ar16+, 2s shell empty. The H2 one-electron capture cross section scales approximately as [EIP (He)/EIP(H2)]2 times the corresponding He cross section, but the shapes of the two cross sections differ in detail. The Arq+ ions were produced by the Cornell superconducting-solenoid, cryogenic electron-beam ion source (CEBIS) and extracted at 2.3 kV. Selected charge states traversed a gas cell, after which they were detected and charge-state analyzed by the energy-retardation method and by a Ï/ â2 cylindrical electrostatic analyzer. The target-gas pressure in the cell was measured directly by the orifice-flow method used for absolute-pressure gauge calibration. The overall error in the Arq+ on H2 cross-section measurements is ±10%, and ±15% in the He measurements.