Nguyen, Tammay K.; (2002) Astrochemistry in interface regions. Doctoral thesis (Ph.D), UCL (University College London).

Text Astrochemistry_in_interface_re.pdf Download (5MB)

Abstract

This thesis is concerned with the chemical modelling of molecular species in a selection of interface layers between astrophysically interesting environments. The aim is to identify 'tracers' for the theoretical scenarios studied, and to try to explain observational data presently available. These tracers can give detailed information concerning the physical conditions in the environment, and may also help to determine its evolutionary status. The ordering of the discussions will reflect the increasingly energetic processes present in each of the different environments studied. Firstly discussed in Chapter 2, is the formation of water ice mantles, in relatively quiescent regions. Using gas-grain chemical models, water ice is studied under a variety of physical conditions. We find that at low Av water ice can be present in clouds at late times or if the cloud is clumpy. Chapters 3 and 4 concentrate on interface layers in progressively more energetic regions. These scenarios range from the mixing of cold molecular gas with warm ionized gas, coupled with the presence of a modestly enhanced ionization rate to the turbulent boundary layers of a diffuse cloud, in which high temperatures and pressures are present. In Chapter 3, we find that at temperatures greater than 100 K, a rich and abundant chemistry can exist. In Chapter 4, we find if an interface layer occupies a few percent of the total column, many polyatomic species in the interface should have detectable abundances. Finally, in Chapters 5 and 6 consideration is moved to the most energetic environments. In Chapter 5, we simulate x-ray ionization in dark clouds and include the formation of C++, and find that the abundance of CH+ is significantly enhanced when C++ is included in the reaction network. In Chapter 6 we study photon dominated regions above disks surrounding main sequence stars and find that the chemical processing produces a large number of tracers with significant column densities.

Download activity - last month

Export as CSVJSONXML

Download activity - last 12 months

Export as XMLJSONCSV

Downloads by country - last 12 months

Export as XMLCSVJSON

Archive Staff Only

View Item