Secondary cluster ion emission from megaelectron volts ion impacts on NaBF4. 1. Ion decay fractions and dissociation pathways
Academic Article
Overview
Research
Identity
Additional Document Info
Other
View All
Overview
abstract
Megaelectron volt ion impacts, event-by-event bombardment/detection, coincidence counting and a time-of-flight (TOF) mass spectrometer equipped with an electrostatic ion mirror were used to study the emission and dissociation of secondary cluster ions sputtered from sodium tetrafluoroborate (NaBF4). The positive and negative plasma desorption spectra produced from NaBF4 are distinct. The negative ion spectrum contains BF4/- and cluster ions composed of Na+ and BF4/-, with a small series of peaks corresponding to (NaF)(n)F-. The positive spectrum, however, is dominated by a cluster ion series with composition (NaF)(n)Na+, n = 0-15. Magic numbers are observed in the positive cluster ion intensity distribution, highlighting n = 4 and 7 as stable cluster compositions. The presence of magic number enhancements in the linear TOF spectrum indicates that the stable cluster compositions are generated prior to entering the drift region of the TOF analyzer (i.e. during ion formation and acceleration). Decay fraction measurements demonstrate that both positive and negative secondary cluster ions carry residual internal energy and undergo dissociation reactions in the drift region of the TOF spectrometer. Decay pathway measurements show that the preferred neutral loss, in general, for positive and negative cluster ions is (NaF)0. In the positive ion mode, the most probable dissociation pathway for many cluster ions is the formation of a product ion with a magic number composition. (C) 2000 Elsevier Science B.V.
