Ultraviolet photochemistry of buta-1,3- and buta-1,2-dienes: Laser spectroscopic absolute hydrogen atom quantum yield and translational energy distribution measurements

摘要

Using pulsed H-atom Lyman- α laser-induced fluorescence spectroscopy along with a photolytic calibration approach, absolute H-atom product quantum yields of φ_(H-b13d) = (0.32±0.04) and φ_(H-b12d) = (0.36±0.04) were measured under collision-free conditions for the 193 nm gas-phase laser flash photolysis of buta-1,3- and buta-1,2-diene at room temperature, which demonstrate that nascent H-atom formation is of comparable importance for both parent molecules. Comparison of the available energy fraction, f_(T-b12d) = (0.22±0.03) and f_(T-b12d) = (0.13±0.01), released as H+ C~4 H~5 product translational energy with results of impulsive and statistical energy partitioning modeling calculations indicates that for both, buta-1,3- and buta-1,2-diene, H-atom formation is preceded by internal conversion to the respective electronic ground state (S~0) potential energy surfaces. In addition, values of σ_(b-1,3-d-Lα) = (3.5±0.2) × 10~(-17) cm~2 and σb-~(1,2-d-L)α = (4.4±0.2) × 10-17 cm~2 for the previously unknown Lyman- α (121.6 nm) radiation photoabsorption cross sections of buta-1,3- and buta-1,2-diene in the gas-phase were determined.