On The Quantum Theory Of The Ramsauer Effec

VOL. 14, 1928 PHYSICS: J. R. OPPENHEIMER 261 ON THE QUANTUM THEORY OF THE RAMSAUER EFFECT BY J. R. OPPENHEIMIRR* NORMAN BRIDGI LABORATORY OF PHYSICS, PASADENA Communicated February 21, 1928 The Ramsauer effect does not correspond to the decrease in optical scattering by a particle when the wave-length of the light is increased. For one may compute the cross-section for elastic collision of an electron with an atom, without making the approximations used by Born. If one does this, and neglects the resonance of the colliding electron with the atomic electrons one finds that, for atoms with no dipole moment in the normal state, the cross-section approaches a finite limit when the electronic velocity is decreased. The only general result of this calculation is that the distribution of scattered electrons tends, in this limit, to become uniform over all angles. If, however, one considers the electronic resonance and spin, one obtains results which seem adequate to account for the effects observed by Ramsauer. Thus one may compute two first order cross-sections for the elastic collision of an electron and a hydrogenic atom, corresponding to initial orbital wave functions respectively symmetric and anti-symmetric in the coordinates of the impacting electron and the atomic electron. These turn out to be of the form jf(v, 6) + g(v, 5)I2 and If(v, 5) - g(V, 5) 12. Here v is the electronic velocity, 5 the angle of deflection; f and g are positive; f corresponds to transitions in which the atomic electron remains undisturbed, and the free electron changes its direction of motion by the angle 5; g corresponds to transitions in which the free electron takes the place of the atomic electron and this latter electron leaves the atom with a velocity v and a direction of motion 6. For fixed 5 and large v, f is much greater than g, while for v =