Relative emission cross sections have been measured for spectral lines in the vacuum ultraviolet region which are produced by collisions of ${\mathrm{He}}^{+}$ with Ar over a range of energies from threshold to 10 keV. The lines investigated arise from the following excited states of Ar and ${\mathrm{Ar}}^{+}$: for Ar, $3p^{5}4s[{}_{}{}^1{}_{}{}^{}P,{}_{}{}^3{}_{}{}^{}P]$; for ${\mathrm{Ar}}^{+}$, $3s3p^6{}_{}{}^2{}_{}{}^{}S$, $3d{}_{}{}^2{}_{}{}^{}P$, $3d{}_{}{}^2{}_{}{}^{}D$, $4s{}_{}{}^2{}_{}{}^{}P$, and $4s^{\prime }{}_{}{}^2{}_{}{}^{}D$. Charge exchange at low collision energies is dominated by transfer into the $3s3p^6$ states. The cross section for exciting this configuration rises rapidly from threshold at 4.7 eV to a low-energy maximum which occurs at 11.3 eV. By normalizing our data to the absolute emission cross section which has been determined by De Heer et al. at a collision energy of 2 keV, it is found that the cross section for exciting the $3s3p^6$ configuration is 5.4 × ${10}^{-17\mathrm{}}$ ${\mathrm{cm}}^2$ at the low-energy maximum. Oscillations are observed in several of the emission cross sections which indicate interferences between the wave functions of one or more of the excited states of the quasimolecule.

• Received 14 January 1974

DOI:https://doi.org/10.1103/PhysRevA.10.117