Absolute Total Scattering Cross Section of He–H2 over the Relative Velocity Range of 2000–3000 m/sec

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Abstract
Absolute helium-hydrogen molecule total cross sections for thermal energy collisions were measured using molecular beams derived from nozzle sources and crossed at right angles. Both nozzles were adjustable in temperature over limited ranges to provide variation in the relative velocities. The absolute density of the target gas (H2) was measured with a capacitance manometer. Over a relative velocity range of 2000–3000 m/sec the cross section, corrected for finite angular resolution, was found to be nearly constant in magnitude averaging 48 Å2. A spherical potential which best fits the experimental data [Lennard-Jones (12, 6), ε=0.7 meV, rm=3.57 Å] was obtained for atom-molecule separations of 2.7–3.3 Å. The range was determined from the response of the cross section to piecewise variation of the theoretical potential. The results are consistent with previously reported theoretical and experimental works.