Observation And Simulation Studies Of Molecular Clouds Chemistry

As we know, molecular clouds are the main birth places of stars. There are more than 200 molecules have been observed in interstellar space with the en-hancements of techniques, which like a good bridge to people to understand the physics and chemistry of molecular clouds. To explain the physical and chemical processes of the observed abundances of molecules, the astro-chemistry has been improved from many aspects, such as theories, experiments and modelings, for many years. These efforts are revealing the mystery of history of interstellar molecules. My thesis review two methods (rotation diagram and population dia-gram analysis) which used to analyze the observed spectral line data of complex organic molecules and the newest status of astro-chemical modeling. This thesis also make a summary of my scientific works during PhD’s study on the analysis of observed abundances of complex organic molecules in EGOs and the microcos-mic physical improvements to astro-chemical models. A outlook of future works is given in the end.Our main results and new findings are:1. The abundances of CH3OH, CH3OCH3, HCOOCH3 and CH3CH2CN observed in Extend Green objects (EGOs) in northern sky are deduced by using population diagram method. The physical and chemical properties of EGOs are also deduced, which hint that they are in the early-stage of massive star-formation. We also compare the observed abundances with results from gas-grain chemical models and find that the models cannot explain the chemistry in EGOs well. Thus, a more suitable gas-grain chemical model is needed for EGOs.2. We write a new gas-grain chemical code with Fortran 90 programming language and a benchemarking of our code has been finished successfully with the 5 typical models addressed in literature.3. The dust grains are assumed in quiescent status in previous gas-grain chemical models. However, the molecular clouds are turbulent which result in the relative velocity of dust grain. To check the effects of dust grain motion, we add it to our gas-grain model and test it in different typical interstellar environments. We find that it can alter the abundances of species by factors up to several orders of magnitude, which may help us to differ the dust grain motion via chemical effects and explain the chemistry better from a new view.4. The previous gas-grain chemical model assume that the dust grains have uniform sizes. However, the dust grains have some forms of grain size distribution addressed in literature through observations, even the dust temperatures are also fluctuant. To check the effects of them to chemistry, we take account the dust grain size distribution, fluctuation of dust temperature and ion accretion into our gas-grain model. Our results show that the abundances of some surface-species can be enhanced by 2-4 orders of magnitude and the consumption of constant areal density becomes invalid. Therefore, grain size distribution and ion accretion are important factors to interstellar chemistry, which may provide new change to interpret the observed abundances of molecules in EGOs.