Vibrational State-Resolved Study of the O- + D2 Reaction: Low-Energy Dynamics from 0.25 to 0.37 eV

We present a study of the particle transfer reaction between O - and D 2 at three collision energies between 0.25 and 0.37 eV. Over this range, the product flux distributions extend over the full range of scattering angles, indicative of collisions in which the atoms remain in close proximity for a significant fraction of a rotational period. The vibrational state populations show the onset of a population inversion, although the partitioning of available energy remains essentially constant at 30%. Vibrationally resolved product angular distributions show that the products formed in the ground vibrational state are distributed with forward and backward peaks, while products excited to v ‘ = 1 are forward peaked. At the lowest collision energy of 0.25 eV, a sharp backward peak in v ‘ = 0 appears and provides evidence for the critical role that collinear collisions play in traversing the OD - ·D saddle point, where bending motion leads to electron detachment. The low-energy dynamics are controlled by the competition between electron detachment and particle transfer as governed by nuclear motion through the electron continuum. A comparison of the vibrational state distributions with “prior” statistical distributions shows that the experimental data extrapolate to a distribution “colder” than statistical at zero kinetic energy, consistent with the conversion of the bending vibrational energy at the OD - ·D saddle point into electron ejection.