Scattering of high-velocity neutral particles. XVIII. He– (CH3F, CH2F2, CHF3)

Fast He beams have been scattered by room-temperature CH3F, CH2F2, and CHF3 to obtain the following average potentials (energy in eV and separation in Å): He–CH3F, V (r) =3.86×102/r8.34, 2.00<r<2.47; He–CH2F2, V (r) =3.88×104/r13.33, 2.22<r<2.58; He–CHF3, V (r) =4.06×105/r15.43, 2.33<r<2.63. Where they overlap, these results agree with independent measurements by Fink, King, and Freeman. The peripheral-force approximation, which assumes that the centers of force in a molecule are located at the nuclei of each atom, has been used to calculate potentials for the above systems from previous measurements on He–CH4 and He–CF4. The calculated potentials are in only fair agreement, being systematically high. Sources of the discrepancies are discussed.