- The photofragmentation of propyne- d 3 , d D 3 C–C≡C–H, D following ∼243.1 nm photodissociation of rovibrationally excited molecules promoted to the second (3ν 1 ) (3ν and third (4ν 1 ) (4ν acetylenic C-H overtone and to the third (4ν CD ) (4ν methyl overtone has been investigated. The resulting H and D photoproducts were detected via (2+1) (2+1) resonantly enhanced multiphoton ionization. The measured room-temperature photoacoustic and jet-cooled action spectra allowed derivation of the molecular parameters of the C-H overtones and the Doppler profiles revealed the translational energies associated with the H(D) photofragments and the H to D branching ratios. Propensities toward the latter were encountered, while the translational energy disposal in both photofragments was essentially identical for a given preexcitation. This behavior agrees with that found for the almost isoenergetic 193.3 nm photolysis of propyne [Qadiri et al., J. Chem. Phys. 119, 12842 (2003)], but contradicts previous findings. The bond fission of C-H and C-D is preceded by internal conversion to, and isomerization on, the ground-state potential energy surface (PES), followed by extensive intramolecular vibrational redistribution. For molecules preexcited to 3ν 1 3ν and 4ν 1 4ν an additional minor channel opens, where elimination of H occurs directly on the accessed excited PES, while that of D on the ground state.