Foil Dissociation of Fast Molecular Ions into Atomic Excited States

We have measured the intensity and polarizations of light emitted from atomic excited states of dissociated molecular ions. The dissociations are induced when fast molecular ions (50-500 keV/amu) are transmitted through thin carbon foils. A calculation of multiple scattering and the Coulomb explosion gives the average internuclear separation of the projectile at the foil surface. Experimentally, we vary the foil thickness to give varying internuclear separations at the foil surface and observe the consequent variation in light yield and optical polarization. Using HeH+ projectiles, we have observed factors of 1-5 enhancements of the light yields from n=3, P,D states of He I and some He II and H I emissions. The results can be explained in terms of molecular level crossings which provide mixings of the various final states during dissociation of the molecular ions at the exit surface. They suggest a short range surface interaction of the electron pick-up followed by a slow molecular dissociation. Alignment measuremerts confirm the essential features of the model. Observations of Lyman ∝ emission after dissociation of H2+ and H3+ show rapid variations in light yield for small internuclear separations at the foil surface.