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

The reaction between ground-state atomic yttrium (a 2 D J ) and ethane (C 2 H 6 ) 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 〈 E coll 〉 = 16.1 kcal/mol to 〈 E coll 〉 = 29.8 kcal/mol. At 〈 E coll 〉 ≥ 18.1 kcal/mol, reactive scattering is observed, with both YH 2 + C 2 H 4 and YC 2 H 4 + H 2 products being formed. Detected products of the YH 2 + C 2 H 4 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) 2 Y(C 2 H 4 ) intermediate. Translational energy distributions for the YC 2 H 4 + H 2 channel, resulting from elimination of H 2 from a common intermediate, demonstrate that a slightly larger fraction of energy available to these products is channeled into translation. The YH 2 + C 2 H 4 channel is found to dominate the H 2 elimination channel by greater than an order of magnitude, which suggests that a small potential energy barrier to the less endoergic H 2 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 YH 2 and YC 2 H 4 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.