- We report the first demonstration of rotational-state selectivity in bond fission. C 2 HD is prepared in the 5 ν 1 vibrational-state and photodissociated by ∼ 243.1 nm photons that also probe the H/D fragments. The production of both H and D is greatly enhanced upon rovibrational excitation and is rotational-state dependent. The H/D branching ratio for the photodissociation of C 2 HD (5 ν 1 ) is 1.5 ± 0.2 for J ′ = 2 and 4.9 ± 0.5 for J ′ = 4. Possible mechanisms for the rotational dependence are discussed.