Scattering of High-Velocity Neutral Particles. XV. He–H2 and He–D2

Total collision cross sections have been measured for helium atoms with energies between 500 and 1900 eV scattered by room temperature H₂ and D₂. Within the experimental precision of ±2% the cross sections of the two systems are identical. The results have been analyzed to obtain the following average potentials: He–H₂: ${\text{V(r)\hspace{0.17em}=\hspace{0.17em}12.11r}}^{\text{−6.07}}\mathrm{eV}\text{, 1.44}\mathrm{\AA }\text{\hspace{0.17em}<\hspace{0.17em}r\hspace{0.17em}<\hspace{0.17em}1.76}\mathrm{\AA }$ ; He–D₂: ${\text{V(r)\hspace{0.17em}=\hspace{0.17em}12.27r}}^{\text{−6.06}}\mathrm{eV}\text{, 1.45}\mathrm{\AA }\text{\hspace{0.17em}<\hspace{0.17em}r\hspace{0.17em}<\hspace{0.17em}1.79}\mathrm{\AA }$ . The measurements are in good agreement with a calculated He–H₂ interaction of Krauss and Mies, suitably averaged over molecular orientation. The effect upon scattering of the anisotropy of the potential is discussed in the light of a classical perturbation theory of small angle scattering developed by Cross.