A CROSSED MOLECULAR-BEAM STUDY OF THE REACTION O(D-1)-]IO+H(HI)

The angular and velocity distributions of the IO product from the reac tion O(D-1) + HI have been obtained in crossed beam experiments at col lision energies, E-c, of 4.7 and 13.6 kcal/mol. The product center-of- mass angular distribution is found to be nearly backward-forward symme tric, with forward scattering favored. The forward to backward scatter ing ratio increases with increasing E-c, from which it is deduced that the reaction occurs via an intermediate complex having a lifetime com parable to its rotational period. Within the ''osculating'' model for chemical reactions, the complex lifetime is estimated to be 4 and 1 ps at low and high E-c, respectively. A large fraction (0.55 at low E-c and 0.46 at high E-c) of the total available energy was found to be re leased into product translational energy. Comparison with the dynamics of the analogous reactions O(D-1) + HCl and O(D-1) + HBr is carried o ut: similarities as well as differences are noted and discussed in ter ms of the potential energy surfaces for reaction. From comparison of s ignal intensities and the previously estimated lower limits to the bra nching ratio of the relative cross sections for XO + H and OH + X chan nels in the O(D-1) + HX (X Cl, Br) reactions, it is concluded that the H-displacement pathway accounts for a significant fraction of the ove rall reaction also in the case of O(D-1) + HI.