Exploring the dynamics of reactions of oxygen atoms in states 3P and 1D with ethene at collision energy 3 kcal mol-1

In a crossed molecular-beam apparatus, we reacted atomic O in states P-3 and D-1 with ethene (C2H4) at collision energy 3 kcal mol(-1). Employing two mixtures, 20% O-2+80% He and 3% O-2+12.5% Ar+84.5% He, as discharge media allowed us to generate two sources of oxygen atoms that have the same mean velocity but different ratios of D-1/P-3 populations, 0.0017 and 0.035. We identified six reactions and recorded time-of-flight spectra of products CH2CHO, CH2CO, and CH3 as a function of laboratory angle. Reaction O(P-3)+C2H4 -> CH2CHO+H has a fraction f(t)=0.43 of energy release in translation, and product CH2CHO has a maximal probability at scattering angle of 140 degrees. For reaction O(D-1)+C2H4 -> CH2CO+2H, f(t)=0.26, and the angular distribution of product CH2CO shows a backward preference. For reaction O(P-3)+C2H4 -> CH2CO+H-2, f(t)=0.35, and the angular distribution of product CH2CO has a slight preference for a sideways direction. In contrast, reaction O(D-1)+C2H4 -> CH2CO+H-2 has f(t)=0.26 and an angular distribution with forward and backward peaking and symmetry. Reactions O(P-3 and D-1)+C2H4 -> CH3+HCO have f(t)=0.09 and 0.08, respectively, and angular distributions with forward and backward peaking and nearly symmetric. The reactivity of O D-1 with ethene is ca. 38 and 90 times that of O P-3 for channels to eliminate H-2 and CH3, respectively. For reactions of O D-1, the branching ratio for elimination of 2H is ca. 3.3 times that for elimination of H-2.