STRUCTURE AND CHEMISTRY IN THE HOT MOLECULAR CORE G34.3+0.15

New multifrequency spatial and spectral studies of the hot molecular c ore associated with the ultracompact HII region G34.3+0.15 have demons trated an extremely rich chemistry in this archetypal hot core and rev ealed differing spatial structure between certain species which may be a dynamical effect of chemical evolution. The structure of the hot co re has been studied with the JCMT in the high excitation 5=19-18 and J =18-17 lines of CH3CN and with the Nobeyama Millimetre Array at 4'' ar e resolution in the J=6-5 transition. Comparison with a VLA NH3(3,3) m ap shows a displacement between peak emission in the two chemical spec ies which is consistent with chemical processing on a time scale compa rable to the dynamical time scale of similar or equal to 10(5) yrs. A 330-360 GHz spectral survey of the hot core with the JCMT has detected 358 spectral lines from at least 46 distinct chemical species, includ ing many typical of shocked chemistry while other species indicate abu ndances that reflect the chemistry of a previous cold phase. The first unambiguous detection of ethanol in hot gas has been made. Observatio ns of 14 rotational transitions of this molecule yield a temperature o f 125 K and column density similar or equal to 2x10(15) cm(-2). This l arge abundance cannot be made by purely gas-phase processes and it is concluded that ethanol must have formed by grain surface chemistry.