Bradley, Caroline Davina (1992) Mechanism of collision-induced decomposition of gaseous multiatomic ions. PhD thesis, University of Warwick.

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Abstract

The mechanism of collision-induced decomposition (CID) has been studied for ions with masses up to 2000 Da. Mass-analysed ion kinetic energy spectroscopy (MIKES) on a large-scale reverse-geometry mass spectrometer was used to measure translational energy losses (AE) by parent ions in collision with inert gas atoms during CID. To avoid ambiguities in mass assignments due to these energy losses, these assignments were made using a four-sector mass spectrometer.

Translational energy losses were found to have different dependencies on collision gas pressure depending on the fragment ion formed. The results suggest that tens of electronvolts of translational energy are lost during each collision between ion and target gas, which is consistent with energy uptake via direct momentum transfer. Multiple collisions are thought not to play a major role in CID of large organic ions. Increasing the incident ion energies from 8 to 25 keV resulted in considerable improvements in fragmentation efficiency, suggesting increased internal energy uptakes. These were more dramatic with increasing incident ion mass.

Comparisons of four-sector tandem mass spectra of the peptides valinomycin and valine-gramicidin A show how additional structural information may be obtained by using a number of different ionisation methods and also different molecule- ions. The use of collision energies of up to 400 eV with argon as target gas on a hybrid mass spectrometer have produced tandem mass spectra which closely resemble those obtained with keV collision energies on the four-sector mass spectrometer using helium as target.
Quasi-equilibrium theory (QET) has been used to calculate the dependence of rate constants on internal energy as the sized of molecule-ions increase. For an ion of mass approximately 1900 Da, QET predicts that internal energies of the order of many tens of eV are required for dissociation to take place within the experimental time-scale.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QC Physics Q Science > QD Chemistry
Library of Congress Subject Headings (LCSH):	Collision spectroscopy, Ions -- Scattering, Collisional excitation, Mass spectrometry
Official Date:	March 1992
Dates:	Date Event March 1992 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	Department of Chemistry
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Derrick, Peter J.
Sponsors:	Science and Engineering Research Council (Great Britain) ; Kratos Analytical (Firm)
Format of File:	pdf
Extent:	xxx, 295 leaves : illustrations
Language:	eng

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