PhD Dissertation Defense

In 1996 the ROSAT satellite discovered x-ray emissions from the atmosphere of comet Hyukatake [1]. Since then Cravens [2] explained these emissions as a result of highly-charged heavy solar wind ions colliding with cometary gas molecules and undergoing charge exchange interactions. Electrons are captured by the incoming ions into excited states. The consequent decays emit photons in the x-ray/vuv range. To study these reactions, ion beams are created in the laboratory and passed through gas targets of CO, an important constituent gas of comet atmospheres. The resulting emissions are studied both the x-ray/vuv (1-70 nm) and the optical (400 – 800 nm) range. Ion beams of different charge states of O, N, C, S, Fe, and Si were used. The data shows that a dominant reaction creating the x-ray emissions is single electron capture and is compared with the predictions of the Classical Over-the-Barrier Model [3], while the dominant reaction creating optical emissions is single electron capture into excited states of the projectile.

1. Lisse C. M. et al., Science, Vol. 274, 205, 1996
2. Cravens T. E., Science, Vol. 296, I 5570, 10 May 2002
3. Niehaus, A. J. Phys. B. 19, 2925