Inelastic collisions between ions and atoms

Charge-exchange cross-sections for H$^{+}$, D$^{+}$, O$_{2}^{+}$, H$_{2}^{+}$, O$^{+}$, CO$^{+}$ and N$_{2}^{+}$ in A; D$^{+}$, O$^{+}$ and N$^{+}$ in Kr; D$^{+}$, C$^{+}$ and Br$^{+}$ in Xe, and O$^{+}$ in H$_{2}$O have been measured between 25 and 4000 eV energy by a method previously described. The normal atomic collision cross-sections rise to a maximum at a voltage which depends on the value of $\Delta $E $\surd $M for the process, M being the atomic mass and $\Delta $E the energy defect of the reaction. Collisions between negative ions and atoms have been studied with the same apparatus, the cross-section of the detachment reaction X$^{-}$ + Y $\rightarrow $ X + e + Y - $\Delta $E being obtained. For S$^{-}$, Br$^{-}$, I$^{-}$, C$^{-}$, P$^{-}$, Li$^{-}$ in Ne, and H$^{-}$ in He, Ne, A, Kr, Xe, this rises with increasing energy of the incident ion. For O$^{-}$ in He, Ne, A, Kr, Xe, Cl$^{-}$ in He, Ne, A, Kr, Xe, and F$^{-}$ in Ne, Kr, Xe the cross-section at low energies is unexpectedly large for the value of $\Delta $E $\surd $M. This may be interpreted as being due to the presence of excited states of these ions, of low electron affinities, in the beam. With O$^{-}$, a low energy electron bombardment source gave smaller cross-sections, i.e. a smaller proportion of excited ions.