Chemistry of massive star formation regions

This thesis discusses abundances of gas and solid phase molecular species in massive star formation regions and compares these abundances to those found in comets. Current chemical models are unable to satisfactorily account for the relative abundances of several molecules observed in many star formation regions. It is thought that this may be due primarily to icy dust mantle contributions in these warm environments. By investigating the chemistry in both phases, it is hoped that a clearer understanding of the connection between dust grains and the gas phase will result.; I present a complete 2.4–25 μm spectrum of the dust-embedded young stellar object W33A. The spectrum was obtained with the Short Wavelength Spectrometer of the Infrared Space Observatory (ISO-SWS) at a mean resolving power of ∼750. The spectrum displays deep H₂O-ice and silicate absorptions centered at 3.0 and 9.7 μm, respectively, together with absorption features identified with various other molecules in the solid phase.; We report new results on the abundances of nitrogen-bearing species in the ices toward W33A. Solid NH₃ is detected for the first time in this line of sight, by means of the inversion-mode feature at 9.0 μm.; This work spawned a study of the mid-infrared spectral regions of 17 objects observed with the ISO-SWS in a search for the presence of the elusive NH₃ solid state absorption features at 2.96 and 9.0 μm. We compare the 3 μm profile with laboratory spectra of pure water and water/ammonia mixtures from the Leiden Molecular Astrophysics database. We determine that the shape of the 3 μm water feature alone does not present conclusive evidence of the presence or lack of NH₃ ice on dust grain mantles due to the large number of unknown physical parameters which influence the 3 μm water profile: grain size distribution, grain shape, mantle composition, thermal history, and geometrical effects.; I also present gas-phase abundances of species found in the organic-rich hot core G327.3-0.6. The data were taken with the SEST telescope. The 1 to 3 mm spectrum of this source is dominated by emission features of nitrile species and saturated organics, with abundances greater than those found in many other hot cores, including Sgr B2 and OMC-1. (Abstract shortened by UMI.)...