Femtosecond Laser Mass Spectrometry (FLMS)

Smith, Derek John (1998) Femtosecond Laser Mass Spectrometry (FLMS). PhD thesis, University of Glasgow.

Abstract

This thesis applies and develops the new experimental technique known as femtosecond laser mass spectrometry (FLMS) to the molecules benzene, deuterated benzene, toluene, naphthalene, benzaldehyde, 1,3-butadiene and carbon disulphide. The procedure couples ultrashort intense pulsed lasers to time-of-flight mass spectrometry (TOP). Similar characteristics are found in the molecular dynamics of all species studied, effectively rendering FLMS as a general technique. FLMS, which combines trace-sensitivity with on-line analysis, has the capability to investigate molecular detection and dynamics, specifically in the exploration of ionisation and/or dissociation pathways with their associated transitional lifetimes, and the mechanisms of such activity. Due to the high ionisation efficiency of FLMS, dominant parent ions and minimal associated fragmentation are observed in the mass spectra, particularly using infrared (IR) compared to ultraviolet (UV) wavelengths. Such molecular fingerprints are advantageous in terms of identification. Moreover, the results have indicated that there is a potential for sensitive uniform analysis. Additionally IR FLMS reveals multiply charged molecular ions with doubly charged parents becoming the second most intense ion present in the mass spectra. Such atomic-like behaviour of medium mass polyatomic molecules is remarkable. The above results are largely in contrast to conventional nanosecond laser studies, with characteristic dissociation and corresponding loss of parent signatures, analytical non-uniformity and non-production of multiply charged species. In such respects FLMS is replacing its nanosecond forerunner. Interpretation of the results is addressed in terms of multiphoton (MPI) and tunnelling (TI) ionisation. At high laser intensities upwards of ~1014 W cm-2, the electric fields are no longer small compared to the binding molecular potential felt by valence electrons and new physical effects are expected. TI is thought to significantly contribute to the ionisation rate, particularly using IR wavelengths, with ionisation following the evolution of the laser pulse profile.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: Kenneth W D Ledington
• Keywords: Applied physics, Optics
• Date of Award: 1998
• Depositing User: Enlighten Team
• Unique ID: glathesis:1998-75891
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 17:39
• Last Modified: 19 Nov 2019 17:39
• URI: https://theses.gla.ac.uk/id/eprint/75891