Scattering of Velocity-Filtered Atomic Beams of Ar and Xe from the (111) Plane of Silver

The scattering of nearly monoenergetic atomic beams of Ar and Xe from the (111) plane of silver has been studied as a function of the nominal velocity ${\upsilon }_0$ transmitted by a slotted‐disk velocity selector (SDVS) used as a velocity filter on the incident thermal‐energy (Maxwellian) beam. The selector has a velocity spread of ${\text{±0.19 υ}}_0$ and studies were carried out over a range of ${\upsilon }_0$ from 2.2 × 10⁴ to 5.3 × 10⁴ cm/sec. The scattered beam distributions were found to be directed, corresponding closely to those of Maxwellian beams when ${\upsilon }_0\mathrm{\hspace{0.17em}=\hspace{0.17em}ῡ\hspace{0.17em}=\hspace{0.17em}}\frac{3}{4}{\text{(2πkT}}_B{\mathrm{\hspace{0.17em}/\hspace{0.17em}M)}}^{\text{1\hspace{0.17em}/\hspace{0.17em}2}}$ , the average velocity of the corresponding Maxwellian beam of temperature $T_B$ . These results, together with the results of earlier scattering studies, imply that the thermal motion of the lattice is the dominant factor in producing the spatial dispersion as well as the velocity dispersion in the scattered beam that has been observed by other investigators. The most likely origin of these dispersive effects is the languidness of the collision in the sense used by Goodman to describe gas atom–lattice collisions.