Deflection of CsF molecules by resonant inhomogeneous electric fields

An experiment that tests a novel method for deflecting molecular beams using inhomogeneous resonance fields is described. The idea is easily understood in classical terms. Imagine that the rotating electric dipole moment of a polar diatomic molecule is placed in an electric field. In a static field the $\overrightarrow{\mu }·\overrightarrow{\mathrm{E}}$ interaction averages to zero due to the rotation of the molecule. If, however, the field rotates at the same frequency as the molecule, the field and molecule remain aligned and the $\overrightarrow{\mu }·\overrightarrow{\mathrm{E}}$ interaction does not average to zero. If the field is spatially inhomogeneous, then there is a net force $-\nabla \left(\overrightarrow{\mu }·\overrightarrow{\mathrm{E}}\right)$ on the molecule. This force can be used in making a molecular beam deflector. Resonance deflection of molecules in the $J=0\mathrm{} \mathrm{and} 1$ rotational states of a molecular beam of CsF has been observed. The deflection is produced by passing a collimated molecular beam of CsF through the center of a T${\mathrm{E}}_{111}$ microwave cavity which is oscillating at the $J=0\mathrm{}\to 1$ transition frequency, 11.019 GHz. The deflection of the $J=0\mathrm{} \mathrm{and} 1$ molecules can be detected as a decrease in the undeflected on-axis beam or as an increase in the off-axis beam. The theory of the effect as well as potential applications are also discussed.