Farebrother, Adam John; (2002) Formation of diatomic molecules at surfaces. Doctoral thesis (Ph.D), UCL (University College London).

Text Formation_of_diatomic_molecule.pdf Download (7MB)

Abstract

Molecular hydrogen, H2, is the most abundant molecular species in the universe. It plays a central role in most of the chemistry in the interstellar medium. However, the mechanism of its formation is poorly understood. There is a wide consensus in the astrophysical community that H2 is formed by associative desorption from cosmic dust grains. The dust grains are found in interstellar dust clouds which are at low temperature and pressure. The precise nature of the dust grains is not known but there is spectroscopic evidence for the presence of graphitic carbon. There are, broadly speaking, two mechanisms for associative desorption from surfaces, the Eley-Ridel (ER) and Langmuir-Hinshelwood (LH) mechanisms. In this work the cosmic dust grain has been modelled as a graphite (0001) surface and the ER. and certain aspects of the LH reaction have been investigated. In the study of the ER mechanism a two dimensional potential energy surface was calculated using density functional theory. Quantum reactive scattering calculations were performed on this surface to determine the probability of the formation of H2 on graphite (0001) and the population of the vibrational states in the product H2. An investigation of the LH mechanism focussed mainly on the diffusion step of the mechanism. To this end, a model potential which incorporates the corrugation of the graphite (0001) surface via a Fourier representation was employed within a Feynman path integral based quantum transition state theory to determine the diffusion constants for H graphite (0001) at a range of temperatures.

Download activity - last month

Export as XMLJSONCSV

Download activity - last 12 months

Export as JSONXMLCSV

Downloads by country - last 12 months

Export as XMLJSONCSV

Archive Staff Only

View Item