State-to-state differential cross sections for the reaction F+D2 at 90 meV:: A crossed molecular beam experiment and a quantum mechanical study

The F + D-2 --> DF + D reaction has been investigated in a high resolution crossed molecular beam scattering experiment at a collision energy of 90 meV (2.07 kcal/mol). Time-of-flight spectra of the DF products have been measured covering the backward hemisphere of center-of-mass scattering angles (theta(cm) = 90 degrees-180 degrees). The energy resolution achieved in the spectra, as good as 20 meV, together with a careful calibration of the beam source intensities and detector sensitivity makes it possible to determine absolute differential and integral cross sections resolved in vibrational and rotational states of the DF products. Interestingly, the backward scattered DF(v(f) = 2) and DF(v(f) = 3) vibrational products are found to present double-peaked (i.e., bimodal) rotational distributions. A three dimensional quantum mechanical calculation of the title reaction performed on the recent ab initio potential energy surface of Stark and Werner [J. Chem. Phys. 104, 6515 (1996)] is presented, which was carried out in the reagents arrangement channel within the coupled-states approximation, employing negative imaginary potentials. The calculated state-to-state differential cross sections show a very encouraging overall agreement with those evaluated from the scattering experiment. In particular, the bimodal structure of the rotational distributions is qualitatively well accounted for in the calculation. However, significant differences still persist between the calculated and the experimental results. (C) 1998 American Institute of Physics.