STATE-TO-STATE DYNAMICS OF ATOM+POLYATOM ABSTRACTION REACTIONS .2. THE H+C2H6/C3H8-]H2(V',J')+C2H5/C3H7 REACTIONS

The rotational and vibrational quantum state distributions for the H-2 products of the H + HR -->H-2 + R reactions (HR = C2H6 and C3H8) at 1.6 eV collision energy have been measured using coherent anti-Stokes Raman scattering. Total reaction cross sections have also been determined. For the total cross sections we find 1.5 +/- 0.5 angstrom 2 for the ethane reaction and 2.9 +/- 0.8 angstrom 2 for the propane reaction. Although several vibrational states are energetically accessible, we observe H-2 products are on average rotationally cold as well, and 20% or less of the total energy is partitioned to H-2 internal energy. However, the quantum state distributions show a positive correlation of H-2 products rotational and vibrational energy. That is, the average rotational energy of the H-2 in upsilon' = 1 is substantially greater than the average rotational energy of the H-2 in upsilon' = 0. Comparison with state-to-state dynamics results previously obtained for the kinematically and energetically similar H + CD4 --> HD + CD3 and H + HCl --> H-2 + Cl reactions seems to indicate that this anamalous energy disposal is an intrinsic characteristic of H + alkane hydrogen atom abstraction reactions at high collision energy. We speculate that this anomalous behavior is the result of inelastic encounters between the nascent H-2 and alkyl radical products in the reaction exit channel.