Crossed-beam radical-radical reaction dynamics of O(3P)+C3H3-->H(2S)+C3H2O.

The radical-radical oxidation reaction, O(3P)+C3H3 (propargyl)-->H(2S)+C3H2O (propynal), was investigated using vacuum-ultraviolet laser-induced fluorescence spectroscopy in a crossed-beam configuration, together with ab initio and statistical calculations. The barrierless addition of O(3P) to C3H3 is calculated to form energy-rich addition complexes on the lowest doublet potential energy surface, which subsequently undergo direct decomposition steps leading to the major reaction products, H+C3H(2)O (propynal). According to the nascent H-atom Doppler-profile analysis, the average translational energy of the products and the fraction of the average transitional energy to the total available energy were determined to be 5.09+/-0.36 kcal/mol and 0.077, respectively. On the basis of a comparison with statistical prior calculations, the reaction mechanism and the significant internal excitation of the polyatomic propynal product can be rationalized in terms of the formation of highly activated, short-lived addition-complex intermediates and the adiabaticity of the excess available energy along the reaction coordinate.