Reaction Dynamics of Oxygen Atoms with Unsaturated Hydrocarbons: Primary Radical and Molecular Products, Branching Ratios and Role of Intersystem Crossing

In this talk we will report on our recent investigations of the reaction dynamics of O(3P) with acetylene4, ethylene5, allene6 and methylacetylene7 using the CMB method. By exploiting “soft” electron-ionization we have probed all energetically allowed product channels (up to ten in O+C3H4) and characterized the dynamics, branching ratios and extent of ISC. The BRs for the five competing channels leading to H+CH2CHO, H+CH3CO, H2+CH2CO, CH3+HCO, and CH2+HCHO from O+C2H4 are analyzed together with those obtained from kinetics studies at room temperature8 (Ec 0.9 kcal/mol). The combined kinetics and dynamics results have allowed us to examine the BRs and the extent of ISC in a wide range of Ecs (temperature), from ~1 kcal/mol (300 K) up to ~13 kcal/mol (4300 K). Experimental results are compared with those of available statistical calculations on ab initio PESs for all systems and with those of quasiclassical trajectory surface-hopping computations carried out in a synergic fashion by the group of Bowman on coupled ab initio triplet and singlet PESs for the benchmark multichannel nonadiabatic reaction O+C2H4.