The photochem. of ICN isolated in Ar matrixes has been investigated using UV absorption and laser spectroscopy under a variety of exptl. conditions. Laser excitation of the repulsive ~A continuum gives rise to long-lived near-IR emission from stabilized I and CN fragments in the shallow excited 3P2 potential and to the formation of the INC isomer. The latter is identified by its UV absorption band, which overlaps the ICN UV absorption. A photoinduced equil. is rapidly established between the two species under 250-nm irradn., in line with the interpretation of previously published IR data (Samuni, U. et al. Chem. Phys. Lett. 1994, 225, 391). This equil. can be shifted in favor of either species by the choice of irradn. wavelength. Permanent dissocn. and the stabilization of CN fragments under UV irradn. is also reported, but the dissocn. efficiency depends strongly on exptl. conditions. This observation allows for the reconciliation of conflicting views in the literature on the photostability of ICN in solid argon. [on SciFinder (R)]