MOLECULAR CLUMPS ASSOCIATED WITH ULTRA COMPACT H-II REGIONS

J = 2-1, 3-2 and 5-4 (CS)-S-34 observations have been carried out toward eight ultracompact HII regions that are prominent in ammonia emission. In several cases we find high density (approximately 10(6) cm-3) clumps with mass approximately 2000 M. and size approximately 0.4 pc around the ionized gas. Our results are consistent with the idea that O-B stars form in high density surroundings. The clumps appear to be in virial equilibrium and their size is consistent with that required by the bow shock model for ultracompact HII regions. We discuss predictions of different models for the evolution of HII regions. We also report detections of torsionally excited methanol towards G10.47 and G31.41.