  Cryogenic buffer-gas beams are a promising method for producing bright
sources of cold molecular radicals for cold collision and chemical reaction
experiments. In order to use these beams in studies of reactions with
controlled collision energies, or in trapping experiments, one needs a method
of controlling the forward velocity of the beam. A Stark decelerator can be an
effective tool for controlling the mean speed of molecules produced by
supersonic jets, but efficient deceleration of buffer-gas beams presents new
challenges due to longer pulse lengths. Traveling-wave decelerators are
uniquely suited to meet these challenges because of their ability to confine
molecules in three dimensions during deceleration and the versatility afforded
by the analog control of the electrodes. We have created ground state
CH($X^2\Pi$) radicals in a cryogenic buffer-gas cell with the potential to
produce a cold molecular beam of $10^{11}$ mol./pulse. We present a general
protocol for Stark deceleration of beams with large position and velocity
spreads for use with a traveling-wave decelerator. Our method involves
confining molecules transversely with a hexapole for an optimized distance
before deceleration. This rotates the phase-space distribution of the molecular
packet so that the packet is matched to the time varying phase-space acceptance
of the decelerator. We demonstrate with simulations that this method can
decelerate a significant fraction of the molecules in successive wells of a
traveling-wave decelerator to produce energy-tuned beams for cold and
controlled molecule experiments.
