Secondary ion emission from C2H6:H2O ice by fission fragments

Abstract

Water (H₂O) ice is a common constituent of several astrophysical object surfaces; other condensed gases (e.g., CH₄, CO₂, NH₃, and C₂H₆) also occur in specific bodies. Bombarded by cosmic rays, these molecules react among them, generating new molecular species, which are partially ejected to the gas phase via a process called sputtering. In the current work, C₂H₆:H₂O ice is irradiated at an averaged temperature of 100 K by energetic multicharged ions (²⁵²Cf fission fragments of ∼ 65 MeV). The sputtered positive and negative secondary ions are detected and analyzed by time-of-flight mass spectrometry (PDMS-TOF). The projectile-surface collision induces the formation of ionic cluster series (H₂O)_nX (X = H₂O⁺, H₃O⁺, O⁻ and OH⁻), and their yield distribution can be represented by the sum of two decreasing exponentials, suggesting the presence of a two distinct formation processes, one for the low cluster masses and another for the larger ones.