The design and performance of a threshold-photoelectron-photoion coincidence spectrometer for the study of unimolecular decomposition in polyatomic ions

Citation
Dmp. Holland et al., The design and performance of a threshold-photoelectron-photoion coincidence spectrometer for the study of unimolecular decomposition in polyatomic ions, NUCL INST B, 179(3), 2001, pp. 436-454
Citations number
31
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Spectroscopy /Instrumentation/Analytical Sciences","Instrumentation & Measurement
Journal title
NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS
ISSN journal
0168-583X → ACNP
Volume
179
Issue
3
Year of publication
2001
Pages
436 - 454
Database
ISI
SICI code
0168-583X(200108)179:3<436:TDAPOA>2.0.ZU;2-4
Abstract
The design, construction and performance of a threshold-photoelectron-photo ion coincidence (TPEPICO) spectrometer for the study of unimolecular decomp osition in polyatomic ions is described. The spectrometer incorporates a he mi spherical electrostatic energy analyser and a time-of-flight (TOF) mass spectrometer. The entrance lens to the hemispherical analyser has been desi gned to have a high collection efficiency for low energy electrons but to d iscriminate strongly against energetic electrons. This arrangement has resu lted in a resolution of about 3.5 meV being achieved for the threshold elec tron peak recorded at the krypton P-2(3/2) ionisation limit. A pulsed elect ric field is used to extract the ions from the interaction region and prope l them towards the TOF analyser. Computer modelling has been used to trace the electron and ion trajectories through their respective analysers. These simulations have enabled the effective interaction volume to be defined, a nd this has allowed the transmission efficiency of energetic fragment ions, formed through a process which also yielded a threshold electron, to be qu antified. The ion TOF peak shape has been examined as a function of initial kinetic energy and as a function of ion residence time. The contribution o f energetic fragments, having specific initial spatial and directional prop erties, to the TOF peak shape has been determined by tracing the paths of i ndividual ions. The actual performance of the spectrometer is illustrated b y a TPEPICO spectrum of the krypton isotopes. Experimental breakdown curves for furan are presented as an example of the use of the apparatus to study unimolecular decomposition in polyatomic ions. By introducing a delay betw een the detection of the threshold electron and the application of the ion extraction field, breakdown curves can be recorded as a function of ion res idence time in the source region. The procedure for analysing the data is d escribed, and the experimental factors that need to be taken into account t o obtain a meaningful comparison with theoretical predictions are discussed . (C) 2001 Elsevier Science B.V. All rights reserved.