Emission at the Na D lines has previously been observed from the intersection of crossed effusive beams of K and NaCl irradiated by a dye laser at wavelengths form 590nm to 735nm. The three beam signal is attributed to direct photoexcitation of KClNa transition region species. Further interpretation of these experiments is hampered, however, by broad translational and internal energy distributions of reacting partners. Supersonic beams of K and NaCl, both seeded in argon, were developed in order to reduce the distribution of translational and internal energies. It was hoped that insight into the reaction dynamics of the K+NaCl system would be revealed by the difference in collision energy between crossed effusive beams and crossed seeded beams. In addition, the rotational broadening of the K\sb2B\sp1Π\sbu-X\sp1Σ\sbg\sp+ spectrum collapses on cooling and therefore "artifact-clean" frequencies could be probed by the laser. Extensive characterization studies of the seeded beam sources were carried out. Mean velocities of K and NaCl were measured to be 1.3 × 10\sp5 and 1.1 × 10\sp5 cm/sec, respectively. Measurements of the rotational and vibrational energy distributions of K\sb2 present in the potassium beam reveal a rotational temperature of 12 ± 1\sp∘K and vibrational temperature of 77 ± 13\sp∘K. Time of flight experiments demonstrate a translational temperature for NaCl and K beams of 170\sp∘K and 12\sp∘K, respectively. Significant three beam emission at the 589.0nm Na D line is observed at the intersection of crossed seeded reagent beams of K and NaCl irradiated by a dye laser from 610nm to 750nm. This three beam signal is comparable to that previously observed with effusive sources. However, contrary to expectations the photoluminescence of the K beam at 589.0nm when laser excited in the region 610-750nm was much larger than for an effusive source. The seeded source potassium photoluminescence at 589.0nm is an order of magnitude larger than the seeded source three beam signal. In contrast, the three beam signal with an effusive K beam is substantially the largest signal in that system. Nevertheless, the narrow energy distribution of these supersonic sources and their ability to change the collision energy makes them very useful for further probing of the KClNa transition region species.