A special class of molecules that are important to many subfields in molecular dynamics and chemical physics, namely free-radical molecules, now enjoy a significant degree of center-of-mass motion control in the laboratory frame. The example reported in this paper concerns the hydroxyl radical $\left(\mathrm{OH}\right)$, which, after the internal degrees of freedom are cooled in a supersonic expansion, has been bunched, accelerated, and slowed using time-varying inhomogeneous electric fields. In situ observations of laser-induced fluorescence along the beam propagation path allows for detailed characterization of the longitudinal phase-space manipulation of $\mathrm{OH}$ molecules by the electric fields. The creation of a pulse containing ${10}^3–{10}^6$ molecules possessing a longitudinal velocity spread from 2 to $80\mathrm{m}∕\mathrm{s}$ around a mean laboratory velocity variable from $550\mathrm{m}∕\mathrm{s}$ to rest with only a few mm spatial extent represents an exciting and useful experimental capability for exploring free-radical dynamics.

• Received 25 March 2004

DOI:https://doi.org/10.1103/PhysRevA.70.043410