SECONDARY ION FOURIER-TRANSFORM MASS-SPECTROMETRY - A NEW APPROACH TOWARDS THE STUDY OF METAL CLUSTER ION CHEMISTRY

By combining an external Xe+ ion secondary ion mass spectrometry (SIMS) source with a Fourier transform mass spectrometer, a new and versatile instrument has been created that allows the study of sputtered metal cluster ions in great detail. They are transported through the magnetic stray fields via an electrostatic lens arrangement and injected into the ion cyclotron resonance (ICR) cell to be trapped for time spans of the order of seconds. They are thermalized by interaction with a collision gas added through a piezoelectric pulsed valve close to the ICR cell. Typical examples include the mass spectra of In+n, Cu+n and Ni+n which extend up to n = 37, 31 and 25 respectively and contain the expected isotope patterns. The first two spectra are characterized by intensity anomalies confirming that the ions detected are exclusively the most stable net results of all earlier decay processes. Another pulsed valve serves to start chemical reactions with O2, C2H4 and N2. In the case of Cu+n ions, collision-induced dissociation (CID) with O2 as the target gas has been investigated, and a method for selective activation of a single isotope out of the complete pattern is presented. Preliminary results on the chemistry of Ni+n ions with C2H4 indicate a predominance of dehydrogenation. © 1990.