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Title: Prestellar and hot molecular cores : astrochemistry in the early stages of star formation
Author: Von Procházka, Azrael Alžbeta
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2013
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This thesis addresses the problem of complex molecule formation in the prestellar and hot core stages of interstellar star formation. We have enhanced a modified rates chemical code to include calculations of physisorption and chemisorption on interstellar grains consisting of amorphous carbon, graphite PAH particles, para-site PAH particles, and silicates as well as calculations of non-thermal desorption via cosmic ray heating, H2 desorption, and cosmic ray-induced photodesorption. We incorporate a time-dependent, warm-up parameter in order to self-consistently treat the chemistry of our dark cloud and hot core models. We find that different dark cloud species achieve better observational agreement for different desorption conditions and that molecules which are inefficiently destroyed in the dark cloud tend to demonstrate an enhanced presence in the early chemistry of the hot core. During the warm up, we observe temporary enhancement of a number of species on the grain surface and • suggest this is due to the physical cycling of molecular material between the gas and solid states as well as the presence of fast barrier-possessing reactions which occur between particles on the grain surface. The presence of a time-dependent warm up also allows a transient period of N-rich chemistry to occur in the gas phase and indicates a number of possibilities which may ::allow the simultaneous occurrence of cyanide and complex organic species in star-forming molecular clouds. We argue that for high NH3 abundances, alkyl-cation transfer reactions may proceed sufficiently rapidly that complex organic species and nitriles can coexist in both compact and ultra-compact hot molecular cores.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available