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 ³P and ¹D with ethene (C₂H₄) at collision energy 3 kcal mol^-1. Employing two mixtures, 20% O₂+80% He and 3% O₂+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 ¹D/³P 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(³P)+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°. For reaction O(¹D)+C₂H₄→CH₂CO+2H, f_t=0.26, and the angular distribution of product CH₂CO shows a backward preference. For reaction O(³P)+C₂H₄→CH₂CO+H₂, f_t=0.35, and the angular distribution of product CH₂CO has a slight preference for a sideways direction. In contrast, reaction O(¹D)+C₂H₄→CH₂CO+H₂ has f_t=0.26 and an angular distribution with forward and backward peaking and symmetry. Reactions O(³P and ¹D)+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 ¹D with ethene is ca. 38 and 90 times that of O ³P for channels to eliminate H₂ and CH₃, respectively. For reactions of O ¹D, the branching ratio for elimination of 2H is ca. 3.3 times that for elimination of H₂. [ABSTRACT FROM AUTHOR]