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The antisymmetric C–H stretching vibration $ \nu _3 $ ν 3 ( $ {}^2\Pi \leftarrow {}{}^2\Pi $ 2 Π ← 2 Π) of ionised acetylene, $ {\rm C}_2{\rm H}_2^+ $ C 2 H 2 + , has been revisited using a cryogenic 22-pole ion trap machine. Two action spectroscopic techniques, the novel leak-out spectroscopy (LOS) method and the more established laser-induced reactions (LIR) method, are applied and compared. Mass selectivity and cryogenic temperatures down to 4 K enabled the observation of uncontaminated spectra in which the Λ-doubling components of this open-shell molecule are mostly well resolved, leading to a slight refinement of the spectroscopic parameters. [ABSTRACT FROM AUTHOR]

[Display omitted] • The 22-pole trap machine COLTRAP investigates ionic complexes at low temperature. • The IR spectra of CH+-He and CH+-He 4 have been measured with ro-vibrational resolution. • CH+-He is confirmed to have a T-shaped structure; its rotational spectrum is predicted. • CH+-He 4 is confirmed to have a 4-membered He-ring around the CH+-axis. A cryogenic 22-pole ion trap apparatus is used in combination with a table-top pulsed IR source to probe weakly bound CH+-He and CH+-He 4 complexes by predissociation spectroscopy at 4 K. The infrared photodissociation spectra of the C–H stretching vibrations are recorded in the range of 2720–2800 cm−1. The spectrum of CH+-He exhibits perpendicular transitions of a near prolate top with a band origin at 2745.9 cm−1, and thus confirms it to have a T-shaped structure. For CH+-He 4 , the C-H stretch along the symmetry axis of this oblate top results in parallel transitions. [ABSTRACT FROM AUTHOR]

The ν 7 antisymmetric C–H stretching fundamental of c- C 3 H 2 + has been characterized in a cryogenic 22-pole ion trap by a novel type of action spectroscopy, in which the rovibrational excitation of c- C 3 H 2 + is detected as a slowing down of the low-temperature reaction c- C 3 H 2 + + H 2 → C 3 H 3 + + H. Ninety-one rovibrational transitions with partly resolved fine structure doublets were measured in high resolution. Supported by high-level quantum chemical calculations, spectroscopic parameters were determined by fitting the observed lines with an effective Hamiltonian for an asymmetric rotor in a doublet electronic ground state, X ˜ A 1 2 , yielding a band origin at 3113.6400(3) cm−1. Based on these spectroscopic parameters, the rotational spectrum of this astronomically important molecule is predicted. Image 1 • The 22-pole trap machine COLTRAP investigates molecular ions at low temperature. • The ν 7 vibrational fundamental of c- C 3 H 2 + has been measured in high resolution. • The ground state spectroscopic parameters of c- C 3 H 2 + have been derived. • The pure rotational spectrum of c- C 3 H 2 + is predicted. [ABSTRACT FROM AUTHOR]

The antisymmetric C–H stretching vibration ν 3 ( 2 Π ← 2 Π ) of ionised acetylene, C 2 H 2 + , has been revisited using a cryogenic 22-pole ion trap machine. Two action spectroscopic techniques, the novel leak-out spectroscopy (LOS) method and the more established laser-induced reactions (LIR) method, are applied and compared. Mass selectivity and cryogenic temperatures down to 4 K enabled the observation of uncontaminated spectra in which the Λ-doubling components of this open-shell molecule are mostly well resolved, leading to a slight refinement of the spectroscopic parameters. [ABSTRACT FROM AUTHOR]