Ammonia in Orion.

Radio observations of the (1, 1), (2, 2), and (3, 3) metastable lines of NH3 in the Orion Nebula are reported. The NH3 line emission is separated into two spatial components, a background ridge and an unresolved core. It is shown that the background is probably the same ridge detected in CO and other molecules and that the unresolved core is centered on the IR cluster in the Kleinmann-Low nebula. The core source is found to consist of three velocity components: (1) a strong narrow optically thick feature at an LSR velocity of 9 km/s and with a rotation temperature of about 60 K; (2) a weaker narrow feature at an LSR velocity of 3 km/s that appears to be optically thin and to originate in a hot region with a rotation temperature in excess of 200 K; and (3) a broad line with a width of approximately 50 km/s and a rotational temperature of about 40 K. An upper limit of 20 arcsec is placed on the size of the emission region for the narrow-line component at 9 km/s, and a lower limit of 350 is obtained for the (N4-14)H3/(N-15)H3 ratio, which is close to the terrestrial value of 279.