Butadiene monoxide (BMO) undergoes the S₀→S₁ transition, involving the excitation of both p and n electrons to p* orbital, at 193 nm. After relaxing to the ground electronic state via internal conversion, BMO molecules undergo intramolecular rearrangement and subsequently dissociate to form unexpected OH radicals, which were detected state selectively by laser-induced fluorescence technique, and the energy state distribution was measured. OH is produced vibrationally cold, OHn" = 0,J", with the rotational population characterized by a rotational temperature of 456±70 K. The major portion (~60%) of the available energy is partitioned into internal degrees of the photofragments, namely, vibration and rotation. A considerable portion (25%–35%) also goes to the relative translation of the products. The Λ doublet and spin-orbit ratios of OH were measured to be nearly unity, implying statistical distribution of these states and, hence, no preference for any of the Λ doublet (Λ⁺ and Λ⁻) and spin-orbit (II_3/2 and II_1/2) states. Formation time of the nascent OH radical was measured to be <100 ns. Different products, such as crotonaldehyde and methyl vinyl ketone, were detected by gas chromatography as stable products of photodissociation. A reaction mechanism for the formation of all these photoproducts, transient and stable, is proposed. The multiple pathways by which these products can be formed have been theoretically optimized, and energies have been calculated. Absorption cross section of BMO at 193 nm was measured, and quantum yield of OH generation channel was also determined.