The rate coefficients for electron transfer from Ar and ${\mathrm{H}}_2$ to ${\mathrm{Ar}}^{\mathit{q}+}$ ions (3≤q≤6) have been measured using an ion-storage technique in a Penning ion trap. The ions were produced in the trap by K-shell photoionization of Ar atoms, using broadband synchrotron x-ray radiation. K-electron removal resulted in vacancy cascading, yielding a distribution of argon-ion charge states peaked near ${\mathrm{Ar}}^{4+}$. The stored ion gas had an initial temperature near 480 K. The basic data determining the rate coefficients k(${\mathrm{Ar}}^{\mathit{q}+}$) are the storage time constants of each charge state in the trap, in the presence of a measured pressure of target gas. The results of the measurements (in units of ${10}^{\mathrm{-}9}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{\mathrm{-}1}$) are k(${\mathrm{Ar}}^{3+}$,${\mathrm{H}}_2$)=4.3(0.7), k(${\mathrm{Ar}}^{3+}$,Ar)=1.6(0.2), k(${\mathrm{Ar}}^{4+}$,${\mathrm{H}}_2$)=5.2(0.6), k(${\mathrm{Ar}}^{4+}$,Ar)=2.5(0.3), k(${\mathrm{Ar}}^{5+}$,${\mathrm{H}}_2$)=5.9(0.7), k(${\mathrm{Ar}}^{5+}$,Ar)=2.9(0.3), k(${\mathrm{Ar}}^{6+}$,${\mathrm{H}}_2$)=8.5(1.2), and k(${\mathrm{Ar}}^{6+}$,Ar)=2.5(0.3).

• Received 8 November 1991

DOI:https://doi.org/10.1103/PhysRevA.45.6379