Abstrakt
A new instrument is under development which is able to guide and store anions and to detect simultaneously electrons using the superposition of suitable RF and magnetic fields. It is based on a modular design combining (i) an rf storage ion source with mass spectrometer, (ii) an octopole ion guide or alternatively a temperature variable 22PT (iii) an electron spectrometer based on magnetic adiabatic collimation, and (iv) a channeltron electron multiplier (CEM) detector.
All modules are transparent in axial direction and, therefore, the ions can be exposed to a beam of photons or of neutrals, e.g. also an H-atom beam. This allows us to study photo detachment of electrons from trapped anions and the interaction of anions with neutrals.
A first successful test has been the observation of the decay time of an H- ensemble exposed to a 532 nm laser. At laser powers of a few mW, storage times are a few s in accordance with the known detachment cross section.
Similar loss rates have been measured by exposing the H- ions to a beam of H-atoms, i.e., via the formation of H2 + e- products. This contribution discusses the instrument and the ongoing activities, the measurement of absolute rate coefficients for H- + H as a function of temperature.
Long term objectives include to detect the emitted electrons with a CEM detector, utilizing the guiding features of the magnetic bottle principle. The ultimate goal is the determination of the energy distribution of the electrons produced via photons or via associative detachment.
Theoretical estimates, accounting for both the rf and the magnetic field, indicate a transmission probability of nearly 100 % and an energy resolution of better than 100 meV.