Vibrational Excitation in Electronically Excited Ions Produced by Charge Exchange

The charge-exchange reactions between ${\mathrm{Ar}}^{+}$ or ${\mathrm{Kr}}^{+}$ and several molecules have been studied spectroscopically. Light emission is observed from the molecular ions, indicating near-resonant charge exchange. Measurements on mixtures of gases provide relative cross sections for the formation of electronically excited ions. The cross sections are largest for the smallest energy defect, in agreement with the theory of Rapp and Francis. The Franck-Condon principle is not a dominant factor in determining the populations of different vibrational levels of diatomic ions, but it may be important for triatomic ions.