  We present two methods for studying reactive collisions between two atomic or
molecular species: a collinear merged-beam method, in which two gas pulses from
a single supersonic beam source are coalesced, and an intrabeam-scattering
technique, in which a single gas pulse is used. Both approaches, which rely on
the laser cooling and deceleration of a laser-coolable species inside a Zeeman
slower, can be used for a wide range of scattering studies. Possible
experimental implementations of the proposed methods are outlined for
autoionizing collisions between helium atoms in the metastable
$2^3\mathrm{S}_1$ state and a second, atomic or molecular species. Using
numerical trajectory calculations, we provide estimates of the expected on-axis
detection efficiency, collision-energy range and collision-energy resolution of
the approach. We have experimentally tested the feasibility of such an
experiment by producing two gas pulses at very short time intervals, and the
results of these measurements are detailed as well.
