Surface-induced reactions of polyatomic ions and cluster ions

Abstract

We have recently constructed the tandem mass spectrometer set-up BESTOF (consisting of a B-sector field combined with an E-sector field, a surface and a time of-flight mass spectrometer) which allows the investigation of ion/surface reactions with high primary mass and energy resolution, i.e. energy spreads of as low as 80 meV fwhm have been achieved. Using BESTOF we have extended previous investigations in several respects. Firstly, we have revisited previously investigated surface-induced reactions of various polyatomic ions including the acetone ion, the benzene ion and interacting with stainless steel surfaces. In addition, we have started to investigate the reactions of polyatomic hydrocarbon ions with carbon tiles from the Tore Supra tokamak in Cadarache. Thirdly, we have investigated surface-induced reactions (using stainless steel and gold surfaces) of fullerene ions as a function of cluster size n and cluster charge state z (up to z = 5) thereby extending previous measurements of Kappes and co-workers for singly charged fullerene ions to multiply charged fullerene ions. Finally, we have extended these fullerene-cluster ion studies to molecular clusters of benzene and acetone. Here we will first describe the characteristics and the performance of this newly constructed tandem mass spectrometer system BESTOF. We will then discuss in an illustrative manner results obtained with this machine selecting as examples the acetone monomer ion and the acetone dimer ions. Besides demonstrating the capabilities of the newly constructed ion/surface interaction apparatus BESTOF and besides illustrating these capabilities by presenting as an example surface-induced dissociations (SID) and surface-induced (pick-up) reactions (SIR) of the acetone monomer ion impacting on a hydrocarbon-covered stainless steel surface, we have here also extended these studies to surface-induced reactions of the acetone dimer ion. In contrast to several pioneering studies involving surface-induced dissociation of cluster ions, we have been here able for the first time to observe and analyse surface-induced (catalysed) reactions (SIR) of cluster ions. In particular, we have been able - as predicted by Cleveland and Landman using molecular dynamics simulations - to observe for the deuterated acetone dimer ion impact on the one hand `collisions which catalyse chemical reactions between cluster constituents' (intra-cluster ion-molecule reactions) leading to the production of the deuteronated acetone monomer ion and on the other hand `collisions between the cluster ion and the surface material' (hydrogen pick-up reactions) leading to the formation of the protonated acetone monomer ion . In competition with these two reactive SIR channels, also the straightforward fragmentation (SID) of the dimer ion into the two fragments could be observed as a minor reaction channel.