Helium Repulsive Potential from Collision Cross Section Measurements

Total collision cross sections have been measured for fast helium atoms, having velocities corresponding to 300–1000 electron volts, scattered in room temperature helium gas. Using classical theory, attempts were made to find a repulsive intermolecular potential which could account for the experimental results. A hard sphere model or a Lennard-Jones type potential were both unsatisfactory, whereas exponential type potentials of the form V(r)=A exp (−arn) seemed promising. For the distances involved in the scattering experiments, 0.55 to 1.05A, the specific repulsive potential which predicted total collision cross sections within the experimental error was V(r)=11.3 exp (−4.63r12)×10−10erg.