  We explore a technique for decelerating molecules using a static magnetic
field and optical pumping. Molecules travel through a spatially varying
magnetic field and are repeatedly pumped into a weak-field seeking state as
they move towards each strong field region, and into a strong-field seeking
state as they move towards weak field. The method is time-independent and so is
suitable for decelerating both pulsed and continuous molecular beams. By using
guiding magnets at each weak field region, the beam can be simultaneously
guided and decelerated. By tapering the magnetic field strength in the strong
field regions, and exploiting the Doppler shift, the velocity distribution can
be compressed during deceleration. We develop the principles of this
deceleration technique, provide a realistic design, use numerical simulations
to evaluate its performance for a beam of CaF, and compare this performance to
other deceleration methods.
