Quasimolecular-state interference studies: Collisions between ions ranging fromLi+toAl+and Ne atoms

Abstract

A systematic investigation of the interference of energetically neighboring quasimolecular terms giving rise to oscillatory structure in the total cross sections for diabatic processes has been performed by optical studies of selected spectral lines produced in ion-atom collisions. All ions ranging from ${\mathrm{Li}}^{+}$ to ${\mathrm{Al}}^{+}$ have been used as projectiles with energies varying from 0.1 to 15 keV using Ne as the target. Interference between direct-excitation and charge-exchange collision channels leading to regularly spaced oscillations which are 180° out of phase have been seen in the ${\mathrm{N}}^{+}$-Ne, ${\mathrm{O}}^{+}$-Ne, ${\mathrm{Na}}^{+}$-Ne, and ${\mathrm{Mg}}^{+}$-Ne systems. The behavior of the oscillations present in the total emission cross sections for the $3p$ levels in Ne cannot be accounted for by the theoretical predictions of Ankundinov et al. Strong polarization effects have been seen in the optical radiation from the $3p^{\prime }{\left[\frac{3}{2}\right]}_1$ level in Ne in all systems and for the $3p {}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ level in Mg in the ${\mathrm{Mg}}^{+}$-Ne system. The oscillations in the Ne excitation function are mainly due to the polarization component of the radiation perpendicular to the beam direction for the ${\mathrm{N}}^{+}$-Ne, ${\mathrm{O}}^{+}$-Ne, and ${\mathrm{Na}}^{+}$-Ne systems, whereas the parallel component also plays a dominant role in the ${\mathrm{Mg}}^{+}$-Ne system. The molecular-orbital (MO) model is used to account for the polarization data.