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

Abstract

A cold target recoil-ion momentum spectroscopy (COLTRIMS) mounted on a 3 MV tandetron accelerator is introduced, which is a powerful tool to study atomic and molecular reaction dynamics induced by few-megaelectronvolt (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 (DAQ) system. Using the TOF and position information on the PSDs, the 3-D momenta of recoil ions can be reconstructed. The diameter of the supersonic gas jet is measured to be $1.3~\pm ~0.3$ mm. The TOFs of ${\mathrm{Ar}}_{(1-4)+}$ 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 $1004~\pm ~21$ 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, N2 ${}^{2+}\rightarrow $ N ${}^{+} +$ N+ and N2 ${}^{3+}\rightarrow $ N ${}^{2+} +$ N+, are identified. The kinetic energy release (KER) distribution for channel N2 ${}^{2+}\rightarrow $ 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.