Continuous source of translationally cold dipolar molecules

The Stark interaction of polar molecules with an inhomogeneous electric field is exploited to select slow molecules from a room-temperature reservoir and guide them into an ultrahigh vacuum chamber. A linear electrostatic quadrupole with a curved section selects molecules with small transverse and longitudinal velocities. The source is tested with formaldehyde (H₂CO) and deuterated ammonia (ND₃). With H₂CO a continuous flux is measured of ≈10⁹/s and a longitudinal temperature of a few kelvin. The data are compared with the result of a Monte Carlo simulation.