Cyclopropylidene ketene 2 is generated by ultraviolet irradiation (lambda greater than or equal to 230 nm) of cyclopropanecarbonyl chloride isolated in argon matrices at 15 K. FT-IR spectra of the primary photolysis products (2 and HCl) trapped in the same cage show the formation of molecular complexes. The HCl stretching mode observed at 2793.5, 2739 cm(-1) is shifted to 61 cm(-1) below the frequency of monomeric HCl (2888.0, 2863.5 cm(-1)) in argon matrix. Irradiation of 2 at lambda greater than or equal to 230 nm induces reversible formation of CO and of a new transient assumed to be cyclopropylidene 3. This carbene reacts with HCl trapped in the same cage or gives 1,2-propadiene by intramolecular rearrangement. The kinetic data show that the rate constant of 1,2-propadiene formation is twice as large as that of cyclopropyl chloride formation. To account for the results of matrix isolation experiments the photodissociation of the cyclopropylidene ketene was modeled by ab initio calculation using 6.31G* and "mini" Huzinaga basis sets.