CO infrared stimulated emission has been observed from flash-initiated O3 + XCN (X = I, Br, Cl, and CN) mixtures with SF6 diluent. About 60 P(J) lines of vibrational transitions from 13→ 12 down to 5 → 4 are present. Dilution in SF6 is essential for stimulated emission; rare gas diluents quench laser emission by collisionally deactivating O(1D) to O(3P). Mass spectrometric analysis shows ∼20% conversion of XCN per flash due to reaction with O(1D). The reaction producing vibrationally excited CO† is O(1D) + CN(X2,Σ, v) → CO†(1Σ+, v′) + N(2D), where v ≤ 4 and v′ ≤ 15. Additionally, there may be some contribution to CO† from the reaction of O(1D) with CN(A2π).