The formation of stable molecules such asNH3, NO,N2O, and HCN as well as reactive transient species, e.g., NH,NH2andN3, resulting from the reactions of energetic N atoms with a residual background ofH2Oand hydrogen in cryogenic solidN2matrices at temperatures of 12–27 K has been studied in situ by Fourier Transform Infrared spectroscopy (FTIR). Bombardment of the matrix by N andN2neutrals with estimated energies between 20 and 120 eV produces a concentration ofN3radicals linearly proportional to the beam flux. The lower limit concentration of active N atoms stored in a cryomatrix has been derived from FTIR spectroscopic measurements. ©1997 American Institute of Physics.