Crossed beam study of the rainbow scattering of Hg by I2: Determination of the binding energy of the HgxI2 adduct

Angular distribution measurements of seeded supersonic atomic beams of Hg scattered by a crossed thermal molecular beam of I2 are reported. The experiments have been performed at two average collision energies: E=0.25 and 0.37 eV. The angular distributions show unresolved rainbow maxima, from which the intermolecular potential well depth has been estimated. Several approximate methods of analysis, assuming realistic potential models and utilizing only the location of the rainbow, have yielded well depths in the range 625--680 K. A more reliable determination of epsilon has been carried out by an iterative fitting procedure involving calculation of the entire angular distribution(s). For an assumed Lennard-Jones (12,6) potential, the well depth is 670 +- 25 K. This corresponds to a binding energy for the HgxI2 adduct (i.e., the van der Waals molecule) of 0.058 eV or 5.6 kJ mol-1. The absence of fully resolved rainbow structure in the observed angular distributions is evidence for a significant noncentral component in the intermolecular potential (leading to anisotropic quenching and concurrent inelasticity). (AIP)Quantum-mechanical calculations that use the recent pseudopotentials of Pascale and Vandeplanque were employed to obtain the 3 2P1/2→ 3 2P3/2 fine structure transition cross sections for Na+He, Ne, Ar, Kr, and Xe collisions. The collision energy range investigated was from threshold (0.00213 eV) to 0.5 eV. The cross sections are found to rise rapidly from threshold to a plateau, with the Na+Ar, Kr, Xe systems also exhibiting a large secondary maximum at approximately 0.1 eV. Regular undulatory structure was observed superimposed on all the cross sections except for the Na+Ne system, while resonances caused by quasibound states were found to be most prominent on the Na+Ar system. Thermally averaged cross sections were calculated from 100 to 1000 degreeK and are found to be in reasonable accord with experiment