Empirical potential energy surface for the Hg+I2 reaction

Abstract

The general features of the ground state adiabatic potential energy hypersurface for the Hg+I2 system have been deduced using results of recent molecular beam scattering experiments, spectroscopic and structural data, and electronic state correlation diagrams. The key element of the potential energy surface (p.e.s.) is a deep attractive ’’basin,’’ implied from the reactive scattering data which provided evidence for the existence of a long-lived intermediate complex, believed to be IHgI. This empirical p.e.s. is characterized by the following features: (a) a shallow well in the entrance valley corresponding to the weakly bound (by ∼0.06 eV) van der Waals adduct Hg⋅I2; (b) a subsequent barrier of ∼0.7 eV in the entrance valley due to avoided crossings of diabatic potential curves, followed by a ’’falloff’’ leading to insertion of the Hg(1S0) into the I2(1Σg+) molecule; (c) a deep potential well (−1.45 eV) corresponding to the stable IHgI complex, taken to be gaseous mercuric iodide in its ground electronic state, 1A1(1Σg+); (d) an exit valley with a minimum energy path rising essentially monotonically, with a negligible intrinsic barrier (≲0.03 eV) from −1.45 to +1.15 eV to yield HgI(X 2Σ+)+I(2P3/2); (e) an essentially monotonic exit path rising to the threshold (+1.54 eV) for collision-induced dissociation; (f) a barrier to reaction in the collinear configuration (Hg–I–I) in which IHgI complex formation is sterically precluded.