  We have demonstrated a new, accessible and economical technique, dubbed
photostop, for producing high densities of trappable molecules. Direct
measurements are presented of NO molecules produced with a narrow velocity
distribution centered at zero in the laboratory frame. NO2, initially cooled in
a pulsed molecular beam, is photodissociated such that the recoil velocity of
the NO photofragments cancels out the velocity of the beam. NO(X^2Pi_3/2, v=0,
J=1.5) molecules are observed up to 10 mircoseconds after the dissociation
event in the probe volume at an estimated density of 1E7 cm-3 per quantum state
and at a translational temperature of 1.6 K. Through the choice of suitable
precursors, photostop has the potential to extend the list atoms and molecules
that can be slowed or trapped. It should be possible to accumulate density in a
trap through consecutive loading of multiple pulses.
