H and D release in approx 243.1 nm photolysis of vibrationally excited and 4 v_(CD) overtones of propyne-d_3

摘要

The photofragmentation of propyne-d_3,D_3C-C ident to C-H,following approx 243.1 nm photodissociation of rovibrationally excited molecules promoted to the second (3v_1) and third (4v_1) acetylenic C-H overtone and to the third (4v_(CD)) methyl overtone has been investigated.The resulting H and D photoproducts were detected via (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 3v_1 and 4v_1 an additional minor channel opens,where elimination of H occurs directly on the accessed excited PES,while that of D on the ground state.