We describe an apparatus designed to measure the velocity distribution of products of photoinitiated bulb reactions. A photolytic precursor AX and reactant BC are coexpanded into a vacuum chamber. A photolysis laser initiates the reaction sequence AX + hnu --> A + X, A + BC --> AB + C. The C product is detected by sub-Doppler (1 + 1 + 1) resonance-enhanced multiphoton ionization (2D-REMPI) to yield its three-dimensional velocity distribution. If this technique were to be applied to the AB(upsilon’,J) product, it would be possible to measure the alignment dependence of the state-to-state differential cross section. We present the experimentally determined velocity distribution of H atoms from the photolysis of HI and D atoms from the reaction H + D2 --> HD + D, and we show that our measurements are consistent with previous studies.