Knowledge Bank

The endoergic reaction of ground state Hg atoms with $I2$ has been studied in the vicinity of the reaction threshold via the crossed molecular beam scattering technique. The observed reaction cross section increases monotonically with relative translational energy. Model functionalities for the post-threshold energy dependence of the cross section (convoluted with the experimentally determined distributions of relative translational energy) have been compared with the experimental cross section function to yield a threshold energy of $1.18\pm 0.03eV$, This value implies a lower bound for the dissociation energy $D0$(HgI) of 0.36 eV. Reinterpretation of existing spectroscopic data for HgI via the LeRoy-Bernstein modified Birge-Sponer extrapolation procedure yields a value of $D0(HgI)=0.390\pm 0.021eV$. Combining these results, the barrier for the reverse reaction is deduced to be $0,03-0.04-0.03+0.04$ eV.