The dense molecular envelope around the compact H II region G5.89 - 0.39 (W28 A2)

VLA observations of ammonia in the (J, K) = (2, 2) and (3, 3) inversion transitions toward the compact H II region G5.89 - 0.39 are presented. These observations reveal the presence of a massive and hot molecular envelope that is clumpy and probably undergoing expansion. Overheated or inverted (3, 3) ammonia emission is detected in front of the H II region. The radio continuum map shows bipolar protuberances, suggesting that the ionized gas is flowing out through openings in the molecular envelope.