Hydrogen Atom Scattering: Velocity Dependence of Total Cross Section for Scattering from Rare Gases, Hydrogen, and Hydrocarbons

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Abstract
An apparatus for scattering experiments with thermal energy hydrogen atom beams is described. The atoms are generated by dissociation of H2 in a tungsten‐tube furnace at ∼2700°K, modulated by a mechanical chopper, and velocity selected by deflection in an inhomogeneous magnetic field. After passing through a scattering chamber containing the target gas, the atoms strike a platinum strip bolometer which functions as a catalytic recombination detector (capable of detecting an H beam of ∼5×1010 atoms cm−2· sec−1). Measurements of the velocity dependence of the total collision cross section in the range 3 to 11×105 cm/sec (equivalent to 0.05 to 0.5 eV) are given for scattering of H atoms from the rare gases, H2, CH4, C2H2, C2H4, C2H6, and C(CH3)4. The results show that throughout this range attractive r−6 interactions are still predominant for Xe, C2H4, and C(CH3)4 whereas repulsive interactions are dominant for most of the other gases. The data are compared with calculations based on the Lennard‐Jones (n, 6) potential and with empirical correlations of van der Waals force constants.