Dissociation of N₂ in capture and ionization collisions with fast H⁺ and N⁺ ions and modeling of positive ion formation in the Titan atmosphere

Abstract

Electron capture and ionization cross sections for protons and nitrogen ions incident on N 2 are measured in the energy range 10–100 keV using time of flight (TOF) coincidence counting techniques. In the case of proton impact the formation of N 2 + ions dominates for both electron capture and ionization channels at all energies, whereas for N + ions, the N 2 + formation dominates for electron capture and the dissociative processes for ionization channels. The energy distribution of the fragment products at 20 and 100 keV have also been measured for the first time using the TOF method. These cross sections are useful in the simulation of energetic ions and atoms interacting with Titan's N 2 ‐rich atmosphere. Titan resides primarily within Saturn's magnetosphere where H + and N + ions are the major ions present along its orbit. It is found that the neutralization of these ions by charge exchange does not occur efficiently above Titan's exobase, so energetic particles with large gyroradii penetrate primarily as ions. The ionization rate and energy deposition in Titan's atmosphere by the energetic H + ions observed by the Voyager spacecraft are explained with the help of the present measurements.