Chemical laser techniques have been used to study the photodissociative excitation of cyanide radical by photolysis of methyl isocyanide: CH3NC→h/ωλ≳1550ÅCH3+CN* (A 2Πi) and to identify efficient spin-orbit relaxation of cyanide radical between its A 2Π1/2 and A 2Π3/2 manifolds. Many new chemical laser transitions have been obtained within the cyanide radical 0,0 red band [CN* (A 2Πi, v′=0) →CN(X 2Σ+, v″=0)] by selective cavity Q spoiling with a diffraction grating. In addition, measurements of the relative gain coefficients of grating-tuned laser transitions establish that photochemical reaction branching strongly favors CN* (A 2Πi, v=0) production; other possible product states [e.g., CN* (A 2Πi, v?1) and CN(X2Σ+, v=0)] are minor components (<10%) of the nascent cyanide radical concentration. The observed cyanide radical product state distribution is highly surprising (i.e., highly nonstatistical), signifying that strong dynamical effects govern the process of photodissociative excitation. All available spectroscopic, photochemical, and product energy partitioning data are used to formulate a state-to-state photochemical reaction mechanism for CN* (A 2Πi, v′) production by CH3NC photodissociation.