Infrared investigations of interstellar ices: Infrared identification of 4.62 and 6.86 micron absorption features in spectra of interstellar sources.

摘要

This dissertation describes the interpretation of infrared spectroscopic features recorded by NASA's Infrared Space Observatory (ISO) and reported in the spectra of several interstellar objects (NGC7538: IRS9, RAFGL 7009S, W33A). It has been suggested in the literature that the ammonium (NH 4+) and cyanate (NCO-) ions are responsible for the observed absorption bands at 4.62 and 6.86 microns (2167 and 1468 cm-1, respectively). Our work points to additional contribution from urea to absorption in these regions. Urea also appears to contribute to the 6.06 micron (1650 cm-1) band where absorption by H2O ice dominates. Ammonium cyanate may be responsible for the absorption band observed at 7.69 microns (1300 cm-1) currently assigned to methane. We attempt to establish the origin and mechanism(s) by which relevant molecular species are produced in the interstellar medium.;We propose that HNCO is a key molecule responsible for the formation of complex species on silicate grains in the interstellar medium (ISM). Reactions of HNCO with interstellar molecules such as NH3 and H2O, as well as proton irradiation of pure HNCO ice result in the formation of NH4NCO. Our research extends to spectroscopic studies of the infrared characteristics of NH4NCO and HNCO in the solid phase. We report new findings from investigations of the reactions of HNCO with simple interstellar molecules; accordingly, we describe a previously unreported chemical species, amino formate (H2NOCHO) formed by a reaction of HNCO with H 2O in the presence of an acid, which acts as a catalyst. Silicate grains in the ISM are expected to catalyze similar reactions in the ISM.