Electrostatic velocity filtering is a technique for the production ofcontinuous guided beams of slow polar molecules from a thermal gas. We extendedthis technique to produce pulses of slow molecules with a narrow velocitydistribution around a tunable velocity. The pulses are generated bysequentially switching the voltages on adjacent segments of an electricquadrupole guide synchronously with the molecules propagating at the desiredvelocity. This technique is demonstrated for deuterated ammonia (ND$_{3}$),delivering pulses with a velocity in the range of $20-100\,\rm{m/s}$ and arelative velocity spread of $(16\pm 2)\,%$ at FWHM. At velocities around$60\,\rm{m/s}$, the pulses contain up to $10^6$ molecules each. The data arewell reproduced by Monte-Carlo simulations, which provide useful insight intothe mechanisms of velocity selection.
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