ON THE FORMATION OF OZONE IN SOLAR SYSTEM OXYGEN ICES EXPOSED TO HEAVY IONS

Abstract

Mimicking the bombardment of icy surfaces with heavy ions from solar system radiation fields, solid-phase molecular oxygen (32O2) and its isotope labeled analogue (36O2) were irradiated with monoenergetic carbon (C+), nitrogen (N+), and oxygen (O+) ions in laboratory experiments simulating the interaction of ions from the solar wind and those abundant in planetary magnetospheres. Online Fourier-transform infrared spectroscopy of the irradiated oxygen ices (12 K) showed that the yields of molecular ozone monomer (O3 ∼ 2 × 10−3 molecules eV−1 in 32O2) were independent of the mass of the implanted C+, N+, and O+ ions (Φmax = 4.0 × 1014 ions cm−2). The production of oxygen atoms in the solid was observed in the mid-IR stabilized via the [O3...O] van der Waals complex. We expand on this inference by comparing the ozone yields induced by light particles (e−, H+, and He+) to the heavy ions (C+, N+, and O+) to provide compelling evidence that the abundance of radiolytic products in an oxygen-bearing solid is primarily dependent on electronic stopping regimes, which supersedes the contribution of nuclear stopping processes irrespective of the mass of the particle irradiation in the kinetic energy regime of solar wind and magnetospheric particles.