Study of the optical emission in collisions between rare-gas atoms: spectra of the emitted radiation

Abstract
The optical spectra between 3300 and 8800 AA were studied at collision energies below about 700 eV for He+He, Ne, Ar, Ne+Ne, Ar and Ar+Ar. Relative cross sections for population of the lowest excited states were derived. For He+He the strong excited He(1snl) states with n>or=3 are He(31P) and He(33D). The strongest emission in all cases involving Ne and Ar atoms was due to the decay of the lowest np5(n+1)p levels of Ne and Ar. Considerable excitation of higher levels was observed for He+Ne, He+Ar and Ar+Ar. For the asymmetrical combinations, excitation of the heavier collision partner is always much stronger than that of the lighter particle. From the relative values of the cross sections for excitation of individual angular momentum states of the np5(n+1)p configurations, it is found that rotational coupling is the most important mechanism causing single excitation in the symmetrical systems Ne+Ne and Ar+Ar, and is also important, though not exclusively, for the other combinations studied.