The interaction of atoms and molecules with solid surfaces V―The diffraction and reflexion of molecular rays

The papers already published in this series have been concerned with the interchange of energy between a gas and a solid and the mechanism of evaporation and condensation. In this paper a rather different, nut related, problem is considered, namely, the theory of the reflexion and diffraction of molecular rays from solid surfaces. Frisch and Stern have recently published the results of some accurate experimental work on the reflexion of helium and hydrogen from crystals of LiF and NaF. One striking result they obtained was that the curves giving the intensity of the reflected or diffracted beam contained a number of pronounced minima, and it was shown by Frisch that at these points two of the components of momentum of the reflected or diffracted particle had certain "forbidden" values, which when plotted against one another lay on one of two smooth curves.