A Cold Target Recoil-Ion Momentum Spectroscopy for Atomic and Molecular Reaction Dynamics Induced by Ions at Few-MeV Energies

A cold target recoil-ion momentum spectroscopy mounted on a 3 MV tandetron accelerator is introduced, which is a powerful tool to study atomic and molecular reaction dynamics induced by few-MeV ions. The setup mainly consists of a supersonic gas jet, a time of flight mass spectrometer (TOFMS), three position-sensitive detectors (PSDs), and a data acquisition system. Using the TOF and position information on the PSDs, the three-dimensional momenta of recoil ions can be reconstructed. The diameter of the supersonic gas jet is measured to be 1.3 ± 0.3 mm. The TOFs of Ar(1−4)+ ions are measured under 2 MeV He2+ impact and are proportional to the square root of the mass-to-charge ratio. The TOFMS achieves a mass resolution of 1004 ± 21 at mass m = 40 (Ar+). The fragmentation of nitrogen by electron loss collisions of 1.33 MeV He+ is investigated. Two complete Coulomb fragmentation channels, N22+ → N+ + N+ and N23+ → N2+ + N+, are identified. The kinetic energy release distribution for channel N22+ → N+ + N+ agrees well with previous studies. Systematic studies of impact ionization and fragmentation dynamics of atoms and molecules induced by few-MeV ion beams can be taken up using this setup.