Generation of XUV photons and their application in time-resolved photoelectron spectroscopy

Abstract

To study chemical dynamics of isolated molecules in the gas phase we have used time resolved photoelectron spectroscopy (TRPES). In the work reported in this thesis we have used both a UV and extreme ultra-violet (XUV) probe to study the photodissociation dynamics of methyl-iodide across the A-band. The thesis also discusses the work carried out to develop a semi-infinite gas cell (SIGC) for the generation of the XUV probe by high harmonic generation (HHG). We performed two TRPES experiments on the A-band of methyl iodide, the first experiment excited using either 269 nm or 255 nm and ionised with a multiphoton probe, the second experiment used four pump wavelengths (279 nm, 269 nm 254 nm and 243 nm) and then ionised using a single XUV probe. The states that make up the A-band of methyl iodide are strongly dissociative in character. In both experiments we observe signal that is consistent with a rapid dissociation at all wavelengths except 254/255 nm. At 254/255 nm we observed surprisingly different dynamics with an extended lifetime and a second feature appearing in the photoelectron spectrum at a delay of around 100 fs associated with a shift in the photoelectron peaks to lower binding energies. The cause of the extended lifetime and more complex dynamics is unclear. We suggest the dynamics may be due to increased excitation onto the ¹Q₁ state or vibrational excitation but the cause of the observation is still uncertain. To generate a XUV probe for the TRPES experiments we use HHG from argon gas. The possible use of a SIGC was investigated to try and increase the photon flux of the harmonic closest to ∼ 20 eV. The effect of focus position, cell pressure and laser power was investigated.

More information

Identifiers

ORCID for Russell Minns: orcid.org/0000-0001-6775-2977

Catalogue record

Export record