Determining molecular chirality with femtosecond LASERs

Abstract

More than 200 years since its first discovery Chirality remains one of the most challenging aspects of analytical chemistry. As chiral enantiomers share almost all physical properties they are only distinguishable through interaction with another chiral system, be it chiral molecules or circularly polarised light. Differences in the real and imaginary parts of the refractive index between right and left circularly polarised light are very small, around 0.01%. The result is conventional circular dichroism effects are slow and insensitive, producing asymmetries on the order of 0.1%.

However the PhotoElectron Circular Dichroism effect first measured in 2001 exhibits a large asymmetry in the photoelectron angular distribution on the order of 10%. By coupling this PECD effect with multiphoton ionisation using femtosceond LASERs, it is possible to study the ultrafast dynamics of these chiral molecules.

In this thesis I present a simple device created at QUB that is capable of measuring the PECD effect using stereo-electron detection to directly measure the forward and backward emitted electrons. Using this device, I will demonstrate that PECD is measurable in pharmaceutically interesting molecules for the first time, as well as discovering a new phenomenom in collaboration with the University of Bordeaux, dubbed PhotoElectron Elliptical Dichroism. The possibility of this PEELD technique being used to measure induced, dynamic chirality is trialled. On top of this, we go through the design and evolution of an even smaller, more compact device for measuring PECD.

Date of Award	Jul 2021
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Engineering & Physical Sciences Research Council
Supervisor	Jason Greenwood (Supervisor) & Ian Williams (Supervisor)