Dynamics of H2 and C2H4 Elimination in the Y + C2H6 Reaction

Abstract

The reaction between ground-state atomic yttrium (a2DJ) and ethane (C2H6) has been studied in crossed molecular beams with 157 nm photoionization detection of products. Studies have been carried out at several collision energies, ranging from 〈Ecoll〉 = 16.1 kcal/mol to 〈Ecoll〉 = 29.8 kcal/mol. At 〈Ecoll〉 ≥ 18.1 kcal/mol, reactive scattering is observed, with both YH2 + C2H4 and YC2H4 + H2 products being formed. Detected products of the YH2 + C2H4 channel are found to exhibit very little translational energy, suggesting that there is little or no potential energy barrier above the final product energy to ethylene elimination from an (H)2Y(C2H4) intermediate. Translational energy distributions for the YC2H4 + H2 channel, resulting from elimination of H2 from a common intermediate, demonstrate that a slightly larger fraction of energy available to these products is channeled into translation. The YH2 + C2H4 channel is found to dominate the H2 elimination channel by greater than an order of magnitude, which suggests that a small potential energy barrier to the less endoergic H2 elimination channel exists. In lower collision energy studies, only nonreactive scattering of Y atoms from ethane is found to occur. This observed collision energy threshold behavior for the onset of YH2 and YC2H4 product formation allows determination of the barrier to C−H bond insertion of Y atoms into ethane to be 19.9 ± 3.0 kcal/mol.