We present observations of the (J, K) = (2, 2) and (J, K) = (3, 3) inversion transitions of ammonia, made at 3″ resolution with the VLA, in the direction of the warm molecular cloud associated with the compact H II region G34.3+0.2. The main hyperfine (HF) line of the (2, 2) transition is detected in absorption toward the west and in emission toward the east of the warm cloud. The main HF line of the (3, 3) transition is detected in emission across the whole source. The satellite HF lines of the (2, 2) and (3, 3) lines are observed only in emission. Our data reveal the presence of three distinct regions, with the temperature and density of the gas increasing as the size of the region decreases. The absorption feature arises in a low-density, n(H2) ∼ 104 cm-3, low-temperature, Trot ∼ 18 K, gas in front of the brightest H II region within the complex. We suggest that this gas is part of the extended molecular material, mapped by Heaton and colleagues in 1985, that surrounds the compact H II regions. The (3, 3) mainline emission, which samples warm gas, arises in a molecular disklike structure ∼7″.3 × 2″.8 in size, elongated in a direction oriented ∼ 55° west of north. The emission in the satellite HF lines of the (2, 2) and (3, 3) transitions arises from an ultracompact region, of ∼1″.6 in size, located at the center of the warm cloud and displaced ∼2″ to the east of the head of the bright cometary H II region. The rotational temperature of the ammonia emission rises from ∼70 K at the edge of the disklike structure to about 185 K at the central position. The molecular hydrogen density in the ultracompact core, of ∼7 × 107 cm-3, is ∼100 times higher than the density in the warm halo. We suggest that the warm cloud corresponds to a disk of molecular gas that was formed from the collapse of a massive, rotating fragment embedded in an extended molecular cloud. Most of the mass at the center of this disk collapsed to form a massive star that ionizes the dense gas around it, producing a bright thermal radio source. The dense molecular gas near the recently formed star, heated and compressed by the associated compact H II region, gives rise to the molecular emission from the hot ultracompact core.
