We report the results of spectroscopic measurements on the exhaust plume from a 1 kW NASA Lewis arcjet, operated on simulated ammonia. The strongest emission features consist of the Balmer lines of atomic hydrogen and a number of vibration-rotation bands of the NH radical. From the spectral data, we calculate a heavy particle temperature of about 3000 K at the exit plane, and an electron temperature of 0.30 eV. Measurements of the spatial distribution of these emission features are presented also. We discuss the importance of the measurements to planned laser induced fluorescence experiments.