Total single-electron-capture cross sections for ${\mathrm{H}}^{+}$ from hydrocarbons [${\mathrm{CH}}_4$, ${\mathrm{C}}_2$${\mathrm{H}}_2$, ${\mathrm{C}}_2$${\mathrm{H}}_4$, ${\mathrm{C}}_2$${\mathrm{H}}_6$, (${\mathrm{CH}}_2$${)}_3$, ${\mathrm{C}}_3$${\mathrm{H}}_6$, ${\mathrm{C}}_3$${\mathrm{H}}_8$, ${\mathrm{C}}_4$${\mathrm{H}}_8$] and the oxide (CO, ${\mathrm{CO}}_2$, ${\mathrm{O}}_2$) and fluoride (${\mathrm{CF}}_4$, ${\mathrm{C}}_2$${\mathrm{F}}_6$, ${\mathrm{C}}_4$${\mathrm{F}}_8$, ${\mathrm{SF}}_6$) gases, as well as Ne, have been measured in the projectile energy range 0.8–3.0 MeV. For comparison at 0.8 MeV/u, electron-capture cross-section measurements for 3.2-MeV ${\mathrm{He}}^{+}$ were also made on most of these same gases. These systematic measurements display additivity failure in each ${\mathrm{C}}_{\mathrm{m}}$${\mathrm{X}}_{\mathrm{n}}$ molecular species. A simple geometrical model, used to estimate intramolecular electron-loss probabilities, allowed extraction of ‘‘atomic’’ ${\sigma }_{10}$ values for C, O, F, and S at each projectile energy. These extracted cross sections generally agreed well with total bound-state electron-capture calculations, corrected for the projectile’s energy loss and Coulomb deflection, target electron-shell binding and polarization, and relativistic effects.

• Received 26 December 1984

DOI:https://doi.org/10.1103/PhysRevA.31.2202