Chemistry plays an important role in the study of the physics and evolution of the warm dense Interstellar Medium (ISM). This is found in very different environment, e.g. in the disks around low... Show moreChemistry plays an important role in the study of the physics and evolution of the warm dense Interstellar Medium (ISM). This is found in very different environment, e.g. in the disks around low-mass young stellar objects (YSOs), in the envelopes of massive-YSOs, and in the nuclei of Ultra Luminous Infrared Galaxies (ULIRGS). The excitation temperatures and abundances of the observed molecules provide the observer with a physicochemical snapshot of the regions. The abundances of the molecules depend strongly on temperature, density, radiation field (UV, Infrared, and X-ray) and initial composition of the gas. Infrared spectroscopy is instrumental in the study of dense ISM as many species have transitions in the infrared. Space based instruments, unhindered by the earth atmosphere, allow us to study these. The absorption and emission features are often weak. Therefore a major challenge in using these instruments is to understand the instrumental characteristics and translating that knowledge into usable reduction algorithms. Most of the data used in this thesis are obtained with space based spectrographs, ISO-SWS and Spitzer-IRS, pushing them to their limits. Show less
