F-D-2 STATE-RESOLVED REACTIVE SCATTERING AT 180 AND 240 MEV COLLISIONENERGIES .1. A HIGH-RESOLUTION CROSSED MOLECULAR-BEAM EXPERIMENT

The F + D-2(j(i)) --> DF(v(f),j(f)) + D reaction has been studied in a high resolution crossed molecular beam scattering experiment at colli sion energies of 180 meV (4.1 kcal/mol) and 240 meV (5.5 kcal/mol), th e highest collision energies ever achieved for this system in this kin d of experiments. The product energy resolution in the time-of-light ( TOF) spectra was typically 30 meV and 35 meV, respectively. The vibrat ionally resolved center-of-mass (CM) differential cross sections (DCS) have been extracted from the TOF measurements and the products' angul ar distributions (AD) in the laboratory (LAB) frame. It has been found that, for almost all the final states, the DCS shifts towards lower C M scattering angles as the collision energy increases. At the two coll ision energies studied, the scattering from the highest vibrational st ate accessible for the DF, i.e. v(f) = 4, gives rise to a prominent fo rward peak in the DCS that seems to increase as the collision energy g oes up. Measurements carried out with D-2 molecular beams at different rotational temperatures indicate that the large angle (backward) scat tering increases with the initial rotation of the D-2, in qualitative agreement with theoretical predictions. The rovibrationally state reso lved integral reaction cross sections have been also experimentally de duced. All these results are compared with quasi-classical trajectory (QCT) calculations reported in the following paper of this issue.