Laser-probing the rotational cooling of molecular ions by electron collisions

Abstract

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 the 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.

Main paper: PDFLaTeX with 7 pages, 4 figures. Supplemental material: PDFLaTeX with 26 pages, 11 figures, 5 tables. This article has been accepted by Physical Review Letters

References in corpus (3)

• Accurate determination of the free-free Gaunt factor; I - non-relativistic Gaunt factors
• Radiative rotational lifetimes and state-resolved relative detachment cross sections from photodetachment thermometry of molecular anions in a cryogenic storage ring
• Dissociative recombination of CH${}^{+}$ molecular ion induced by very low energy electrons