Superelastic scattering of electrons from Ar³⁺

A crossed-beams energy-loss spectrometer has been used to study, for the first time, angular distributions for the superelastic scattering of an electron from a positive ion. It is often a distinct disadvantage for collision studies that ECR sources tend to produce ions in a mixture of ground and metastable levels. We have however used this to our advantage to study superelastic scattering from metastables, observing energy gain spectra using an electrostatic hemispherical analyser fitted with a position sensitive detector. First results are presented for Ar³⁺ ions, with observation of the 3s²3p^{3 2}D° metastable state at 2.61 eV above the ground 3s²3p^{3 4}S° level.