Mass spectrometry of impact fragmented polymers: the role of target properties

摘要

When a cosmic dust particle impacts at very high velocities (a few tens of km/sec) it does not only vaporize, but also partially ionizes, leaving a mixture of neutral atoms and molecules, positive and negative ions and electrons. The present work is related to space missions, where Impact Ionization is being used to investigate fast moving cometary, interplanetary or interstellar dust particles. Information about their composition, paying special attention to their organic content, may help to clarify the question of the origins of life. At extreme velocities such as those encountered in the flyby of Comet Halley, around 80 km/s, there is no doubt that the molecules are completely dissociated [1] and consequently only atomic species remain after the impact, which makes it difficult to reliably confirm the existence of organic molecules. Fortunately, at lower velocities at least molecular fragments may survive. The plan of the present study was to perform a Laboratory Study on the impact velocity dependence of the organic molecule fragmentation by measuring the charged components of the gaseous impact products by means of time of flight mass spectrometry. Additionally, we varied the target material's properties in the hope of learning more about the ion formation processes. In this context we investigated the question: Do molecules only break up upon impact or do they also re-form? The projectiles used contained sulphur and we observed how the presence of this "tracer" element shows up in the mass spectra.