The thesis "Carbon, oxygen, and hydrogen isotope fractionation in molecular clouds" is submitted in 2013 to the University of Manchester, by Marion Mathelié-Guinletfor the degree of master of science.Comparison between observations and astrochemical models allows to determinemore precisely the physics and chemistry of an astronomical environment. Oneneeds chemical tools to predict different parameters among which, the age and theunderlying isotope ratios, to help observers focus on what should be the keys todeeply study this environment.This thesis tries to figure out these chemical tools on large scale. It presents theupgrade of a chemical network, which includes the main isotopes of carbon ( 12C,13C), oxygen (16O, 18O) and hydrogen (H, D).The abundance ratios CS/SO and NH3/SO appear to be good chemical clock forearly times (t < 10^5 years) whereas those of NH3/HCN (NH3/HNC) and NH3/HCO+work well for later ages, as their temporal variations are sudden and strong over adefined period of time and for all densities between 10^3 and 10^7 cm^-3. Once dating the environment, other ratios are interesting to determine the carbon underlying ratio: HNC/HN13C, HCO+/H13CO+ and CH+/13CH+. These tools have been applied to study a particular interstellar cloud : the cyanopolyyne peak of the TaurusMolecular Cloud TMC-1 is found to be around 2 *10^5 years, has a density of 2*10^4 cm^-3 and a carbon underlying ratio of 75.Furthermore, the upgraded network is used to predict temporal and densityvariations over time of the isotopologues of HNCO, which is thought to trace eitherdense, far infrared or shocked regions. These strong temporal and density variationsare compared with some basic molecules containing the main elements, such asHCO+.
|Date of Award||31 Dec 2013|
- The University of Manchester
|Supervisor||Andrew Markwick (Supervisor)|
- chemical clock
- isotope fractionation