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Secondary ion emission from condensed CO bombarded by fission fragments

Abstract:

Frozen CO was bombarded by ∼65 MeV fission fragments and the emitted secondary ions were analyzed by time-of-flight mass spectrometry. Target was kept at UHV conditions and its temperature was varied from 25 K up to complete sublimation of the ice film. The observed positive cluster ion series are well represented by the chemical expression (CO)mCn+, where m and n ≥ 0, and the negative ones by Cn- and (CO)mO-. The positive cluster ion series with the highest desorption yield is (CO)2Cn+, in accordance with the particular high binding energy of (CO)2. The total negative ion yield is about 90 smaller than the positive one (2.8 ions/impact) and the main negative ion series observed is Cn-. The desorption yields of the cluster ion series decrease exponentially with the mass of the cluster, and it is proposed that the decay constant, km, characterizes the process. The Cn+ and Cn- series have a fast decay (k m = 0.047 u-1) and should be generated by fast gas-phase reactions in the thermalized nuclear track plasma. The (CO)m+ series presents a slow decay constant (km = 0.007 u -1); its members are probably residues of the fractured solid. Desorption yields depend weakly on target temperature up to near 30 K, when fast sublimation occurs. Fullerene ions were not observed within Y(C 40+) ≤ 2 × 10-4 ions/impact. © 2006 Elsevier B.V. All rights reserved.