Secondary ion emission from CO 2–H 2O ice irradiated by energetic heavy ions : Part II: Analysis–search for organic ions

Abstract

Secondary ion mass spectrometry is used to investigate ion emission from a frozen-gas mixture of CO 2 and H 2O ( T = 80–90 K) bombarded by MeV nitrogen ions and by 252Cf fission fragments. The aim of the experiment is to detect organic molecules, produced in the highly excited material around the nuclear track, which appear as ions in the flux of sputtered particles. Part I of the present work [L.S. Farenzena, V.M. Collado, C.R Ponciano, E.F. da Silveira, K. Wien. Int. J. Mass Spectrom. 243 (2005) 85–93] described the method and presented the time-of-flight mass spectra; a list of the CO 2 specific and H 2O specific reaction products was provided. In Part II, the peaks of the TOF mass spectra are analyzed. Projectile-ice direct coulomb interaction leads to the production in the track of the H +, C +, O +, O 2 +, CO + and CO 2 + primarily ions, which react in the highly energized nuclear track plasma mainly with CO 2 and H 2O or H 2CO 3. The positive molecular hybrid ions formed are identified as organic species like COH +, COOH +, CH n = 1–3 +, H n = 1,2 COOH + and cluster ions. Similarly, the negative primarily ions O − and OH − formed by electron capture produce negative hybrid ions such as (CO 2) n OH −, the four ions (CO 4H m = 0–3 ) − and the corresponding cluster ions. By far, most of the molecular ions have been formed by one-step reactions; exceptions are eventually the CO 4H m − ions created by a reaction between CO 3 − and water molecules. An intense mass line corresponding to HCO 3 + has been observed, but not the one due to formaldehyde ion. Weak signals of ionic ketene, hydrogen peroxide and carbonic acid were seen.