VIBRATIONAL STATE-RESOLVED STUDY OF THE O--2 REACTION - LOW-ENERGY DYNAMICS FROM 0.25 TO 0.37 EV(D)

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 rang e, the product flux distributions extend over the full range of scatte ring angles, indicative of collisions in which the atoms remain in clo se proximity for a significant fraction of a rotational period. The vi brational state populations show the onset of a population inversion, although the partitioning of available energy remains essentially cons tant at 30%. Vibrationally resolved product angular distributions show that the products formed in the ground vibrational state are distribu ted with forward and backward peaks, while products excited to upsilon ' = 1 are forward peaked. At the lowest collision energy of 0.25 eV, a sharp backward peak in upsilon' = 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. T he low-energy dynamics are controlled by the competition between elect ron detachment and particle transfer as governed by nuclear motion thr ough the electron continuum. A comparison of the vibrational state dis tributions with ''prior'' statistical distributions shows that the exp erimental data extrapolate to a distribution ''colder'' than statistic al at zero kinetic energy, consistent with the conversion of the bendi ng vibrational energy at the OD-.D saddle point into electron ejection .