Reaction Hg+I2→HgI+I revisited

The crossed molecular beam study of Mayer et al. (1977) on the subject reaction is revisited. The present work employs a different beam configuration and thus kinematic framework, and a larger range of relative translational energies is covered (i.e., from the threshold of 1.15 to 3.75 eV). Measurements include in-plane angular distributions and relative values of integral reaction cross sections as a function of energy. At low energies, the results of the present experiments are in good agreement with the previous work. Starting at the threshold, the reaction proceeds through the formation of a long-lived complex, presumed to be IHgI. At higher energies, the c.m. angular distributions show a gradual increase of the so-called ''backscattered component.'' This is interpreted as the opening of a new reaction path: the direct-mode abstraction of I via collinear approach of the Hg atom to the I2 molecule. The overall dynamics of this reaction are interpreted in the context of the semiempirical potential energy surfaces and electronic state correlation diagrams of Muckerman et al. (1977). From the present experimental results, the height of the barrier in the exit channel for the collinear configuration can be estimated to be in the range 2.0--2.3 eV. The excitation function rises from threshold and reaches a maximum at collision energy of 2.6 eV, falling off monotonically thereafter