[1] Dissociation and dissociative ionization of molecular nitrogen by solar UV radiation and by photoelectrons and sputtering by the magnetospheric ions and pickup ions are the main sources of translationally excited (hot) nitrogen atoms and molecules in the upper atmosphere of Titan. As Titan does not posses an intrinsic magnetic field, Saturn's magnetospheric ions can penetrate Titan's exobase and sputter atoms and molecules from it. The sputtering of nitrogen from Titan's upper atmosphere by the corotating nitrogen ions and by photodissociation was addressed earlier [Lammer and Bauer, 1993;Shematovich et al., 2001]. Here penetration of slowed and deflected magnetospheric N + and carbon-containing pickup ions is described using a Monte Carlo model. The interaction of these ions with the atmospheric neutrals leads to the production of fast neutrals that collide with other atmospheric neutrals producing heating and ejection of atoms and molecules. Results from Brecht et al. [2000] are used to estimate the net flux and energy spectra of the magnetospheric and pickup ions onto the exobase. Sputtering is primarily responsible for any ejected molecular nitrogen, and, for the ion fluxes used, we show that the total sputtering contribution is comparable to or larger than the dissociation contribution giving a total loss rate of $3.6 Â 10 25 nitrogen neutrals per second.

[1] 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.

[1] We investigate the importance of nitrogen ions within Saturn's magnetosphere and their contribution to the energetic charged particle population within Saturn's inner magnetosphere. This study is based on the Voyager observations of Saturn's magnetosphere and Cassini observations. The latter have shown that water group ions dominate both the plasma and energetic particle populations but that nitrogen ions over a broad range of energies were observed at $5% abundance level. In the outer magnetosphere, methane ions were predicted to be an important pickup ion at Titan and were detected at significant levels in the outer magnetosphere and at Titan. O + ions were found to be the dominant heavy ion in the outer magnetosphere, $60%, with methane ions being $30% of the heavy ions and N + being a few percent. The two major sources of nitrogen ions within Saturn's magnetosphere are Titan's atmosphere and primordial nitrogen trapped in the icy crust of Saturn's moons and its ring particles deep within the magnetosphere. It is important to understand the source, transport, and sinks of nitrogen in order to determine whether they have a primordial origin or are from Titan's atmosphere. The energetic component is important, since it can come from Titan, be implanted into the surfaces of the icy moons, and reappear at plasma energies via sputtering obfuscating the ultimate source. As we will show, such implantation of nitrogen ions can produce interesting chemistry within the ice of Saturn's moons. The emphasis will be on the nitrogen, but the oxygen and other water group ions are also considered. We argue that neutral clouds of heavy atoms and molecules within Saturn's outer magnetosphere may be the dominant source of energetic heavy ions observed within the inner magnetosphere. Pickup heavy ions in the outer magnetosphere have energies $1-4 keV when born. If they diffuse radially inward, while conserving the first and second adiabatic invariants, they can have energies greater than several hundred keV inside of Dione's L shell. We will show how observations relate to the various sources and acceleration processes such as ionization, collisions, wave-particle interactions, and radial diffusion.