The novel iminylradical O2SN, a SO3 analogue, was produced by flash vacuum pyrolysis of gaseous alkyl sulfonyl azides RSO2N3 (R=CF3, CH3) mixed with argon. Photoisomerization (λ>360 nm) of O2SN into planar syn‐OSNO and anti‐OSNO (see picture) was observed in solid noble‐gas matrices.