Solid molecular nitrogen (N-2) may exist in large abundances in various low-temperature interstellar and solar system environments. Intense radiation fields can cause molecular nitrogen ice to undergo chemical alterations by cleaving the nitrogen-nitrogen triple bond. We have simulated this chemical processing by carrying out radiolysis experiments using energetic electrons on molecular nitrogen ice at 10 K that has been labeled with different isotopes. We have identified four isotopologues of the azide radical (N-3) via infrared spectroscopy. The N-14(3) radical was detected by a doublet that has peaks centered at 1657 and 1652 cm(-1). The formation dynamics are also investigated. (c) 2007 Published by Elsevier B.V.