The infrared multiple photon dissociation of NH3 by a CO2 laser is investigated through laser-induced fluorescence and chemiluminescence techniques. A linear dependence of the fractional dissociation yield on pulse energy is found, the dependence exemplifying two distinct thresholds. Significant collisional enhancement of the fractional yield is observed. The results are discussed in terms of the existence of bottlenecks in the laser up-pumping process. © 1979.