Tetrazete (N4). Can it be prepared and observed?

The nitrogen plasma generated by microwave or electrical discharge in gaseous N2 was quenched on a cold window (6.2–35 K) and resulting matrix was examined by IR and UV–Vis absorption spectroscopies. In samples prepared with 14N2 we observe a weak infrared transition at 936.7 cm−1. It shifts to 900.0 cm−1 when 15N2 is used. Both peaks do not correlate with any other features in the spectra and are best explained as originating from tetrahedral tetrazetes (N4). Their positions are compatible with quantum chemical estimates for 14N4, at 936.0 cm−1 and 15N4, at 904.4 cm−1.