title: Two-photon rotational action spectroscopy of cold OH- at 1 ppb accuracy.
abstract: The fundamental rotational transition J = 1←0 of the anion OH(-) has been measured by cooling mass-selected OH(-) ions to 10 K in a 22-pole ion trap and applying a novel rotational-rovibrational two-photon scheme. A transition frequency of (1  123 101.0410 ± 0.0014)  MHz was obtained with so far unprecedented accuracy. The general application of the presented action-spectroscopy scheme to other anions and cations is discussed.
authors.affiliation: I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany.
authors.forename: Pavol
authors.initials: P
authors.lastname: Jusko
authors.affiliation: I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany.
authors.forename: Oskar
authors.initials: O
authors.lastname: Asvany
authors.affiliation: I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany.
authors.forename: Ann-Christin
authors.initials: AC
authors.lastname: Wallerstein
authors.affiliation: I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Brünken
authors.affiliation: I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Schlemmer