Diazophosphane HPN2, a heavy analogue of hydrazoic acid (HN3), has been synthesized at low temperature (10 K) through photolytic reactions of molecular nitrogen (N2) with phosphine (PH3) and phosphaketene (HPCO) under irradiations at 193 and 365 nm, respectively. The characterization of HPN2 and its isotopologues DPN2 and HP15N2 by matrix-isolation IR and UV-vis spectroscopy is supported by quantum chemical calculations at the CCSD(T)-F12a/cc-pVTZ-F12 level of theory. Upon irradiation at 266 nm, the P-N bond in HPN2 breaks, whereas its photolysis at 193 nm generates the elusive phosphinyl radical •PN2.