Isochronous mass spectrometry in an electrostatic storage ring.

For sensitive studies of molecular ions in electrostatic storage rings, the exact knowledge of the isobaric composition of stored beams from a variety of ion sources is essential. Conventional mass-filtering techniques are often inefficient to resolve the beam components. Here, we report the first isochronous mass spectrometry in an electrostatic storage ring, which offers a high mass resolution of Δm/m < 1 × 10-5 even for heavy molecular species with m > 100 u and uncooled ion beams. Mass contaminations can be resolved and identified at relative fractions down to 0.02%.

Laser Probing of the Rotational Cooling of Molecular Ions by Electron Collisions.

We present state-selected measurements of rotational cooling and excitation rates of CH^{+} molecular ions by inelastic electron collisions. The experiments are carried out at a cryogenic storage ring, making use of a monoenergetic electron beam at matched velocity in combination with state-sensitive laser dissociation of the CH^{+} ions for simultaneous monitoring of the rotational level populations. Employing storage times of up to 600 s, we create conditions where electron-induced cooling to the J=0 ground state dominates over radiative relaxation, allowing for the experimental determination of inelastic electron collision rates to benchmark state-of-the-art theoretical calculations. On a broader scale, our experiments pave the way to probe inelastic electron collisions for a variety of molecular ions relevant in various plasma environments.