Filtering slow polar molecules from a thermal gas

The interaction of polar molecules with an inhomogeneous, electrostatic field to filter molecules from an effusive room-temperature source is exploited to create a slow molecule beam. Whether a dipolar molecule is trapped in or expelled from the electric field minimum depends on the orientation of the molecular dipole with respect to the electric field. These molecules are called low and high-field seekers, respectively. Thus, an electric field configuration with a field minimum on axis acts as a 2-dimensional trap for low-field seeking molecules with small transverse velocity components. A linear quadrupolar is opted, which is one of the simplest suitable geometries. The longitudinal velocity is limited by a bent section, where the centripetal force due to the radius of curvature and electric field gradient guide only the slowest molecules around the bend.