Cluster ions and multiply charged ions formed in frozen CO2 molecules under heavy ion impact

O_{2}^{+} Production Coming from CO_{2} Single-Event Electron Impact

In CO_{2}-rich atmospheres that are always exposed to ionizing radiation (e.g., Venus and Mars), every fragmentation process can significantly impact the inventory of moieties present in these environments. Nevertheless, the production of O_{2}^{+} ions as a direct result of CO_{2} fragmentation has never been quantified so far. Since molecular oxygen is considered as a potential trace of living organisms, nonbiotic pathways for its production must be known. In this work, O_{2}^{+} coming from CO_{2} fragmentation by electron impact is unambiguously identified and measured in absolute scale.

Electronic sputtering produced by fission fragments on condensed CO and CO2

Condensed CO and CO2 are bombarded by approximately 65 MeV 252Cf fission fragments and the desorbed ions are analyzed by time-of-flight mass spectrometry as a function of target temperature, in the ranges 25-33 K and 75-91 K, respectively. Absolute desorption yields are measured up to complete ice sublimation. The mass spectra of both ice targets reveal the emission of: (1) low mass ions, produced by direct Coulomb interaction of the highly charged projectiles and delta-electrons with CO and CO2, and (2) pronounced series of cluster ions. The basic ice cluster structures (CO)n and (CO2)n are present in the emitted cluster series such as (CO)nCO+, (CO2)nCO2+, or (CO2)nCO3-. In the case of CO ice, however, the intense production of the series Cn+, Cn-, and (CO)mCn+ shows that Cn is the main cluster structure, consequence of a higher concentration of free carbon atoms in the nuclear track plasma of CO ice than in that of CO2 ice. Ion cluster abundance is observed to decrease exponentially with cluster mass. The decay constant is k(n) congruent with 0.13, about the same for series based on (CO)n and (CO2)n, but a factor 3.3 higher for the Cn series. The Cn clusters are formed by gas-phase condensation, but the (CO)n and (CO2)n clusters are produced by fracturing of the highly excited solid around the nuclear track. A dramatic reduction of the ion desorption yield is observed near T = 29 K for CO and near T = 85 K for CO2, when fast sublimation occurs and ice thickness vanishes. Close to sublimation temperature, the decay constant of the (CO)2Cn+ series increases due to a decreasing formation probability of large Cn clusters.