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.

arXiv commentMain 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

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