Investigation of the interaction potential between a neutral molecule and a conducting surface

The interaction potential between a neutral molecule and a conducting surface is investigated through the study of the deflection of a beam of molecules by the conducting surface. The ultrahigh-vacuum system gave a vacuum below 5×${10}^{-11\mathrm{}}$ Torr, where the scattering by the residual gas is negligible in the deflection region of interest. An $r^{-3\mathrm{}}$ potential is predicted from a model in which the permanent dipole of the molecule interacts with its image in the surface of an ideal conductor. The measured deflection by the conducting surface does not agree precisely in form with this predicted potential. When this small difference in form is ignored, the observed interaction constants indicate that the model does, in fact, account for the major part of the interaction. These observed constants are from 0.42 to 0.68 of the predicted values. There remain unevaluated corrections arising from the finite resistivity of the conductor, and from a contribution by the fluctuation of the instantaneous dipole moment of the molecule from its statistical average (i.e., the permanent dipole moment).