Matrix isolation infrared observation of N3 using a nitrogen microwave discharge plasma source

The asymmetric stretching band of the N₃ radical in a nitrogen matrix at 1657.5?cm^?1 has been observed by directing the output of a nitrogen microwave discharge plasma source onto a CsI window at 12?K. The identification and assignment of this band to the N₃ radical has been accomplished by performing isotopic experiments, matrix annealing experiments, and photolysis experiments. The observed N₃ band positions are compared to literature frequencies observed in matrix isolation experiments using other generation sources and to literature theoretical frequencies calculated using high level ab initio and density functional theory methods. Temperature-dependent deposition experiments (10–20?K) and additional isotopic discharge plus co-deposition experiments are also performed in an effort to determine if the N₃ radical is being formed in the gas phase or by matrix surface reactions, and in order to gain insight into the reaction mechanism. After considering all of the mechanistic evidence (temperature-dependent and isotopic discharge/co-deposition spectra, theoretical reaction energetics, gas phase reaction kinetics, isotopic N₃ distributions), it is concluded that the N₃ radicals are being formed from the reaction of N(²D) atoms with vibrationally excited N₂ molecules in the nitrogen matrix via a linear (end-on) pathway.