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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]

The ro-vibrational and pure rotational spectra of the linear ion HC3O+ have been investigated in a 4 K cryogenic ion trap instrument. For this, a novel action spectroscopic technique, called leak-out-spectroscopy (LOS, Schmid et al., J. Phys. Chem. A 2022, 126, 8111), has been utilized and characterized. In total, 45 ro-vibrational transitions within the fundamental band of the ν1 C–H stretching mode were measured with a band center at 3237.132 cm−1, as well as 34 lines from the combination band ν2 + ν4, and 41 lines tentatively identified as the combination band ν2 + ν5 + ν7, interleaved and resonant with ν1. Surprisingly, also two hot bands were detected despite the cryogenic operation temperature. Based on the novel action spectroscopy approach, a new double-resonance rotational measurement scheme was established, consisting of rotational excitation followed by vibrational excitation. Seven rotational transitions were observed between 89 and 180 GHz. Highly accurate spectroscopic parameters were extracted from a fit using all available data. In addition, a pulsed laser system has been employed to record a low resolution vibrational spectrum, in order to demonstrate the compatibility of such lasers with the LOS method. [ABSTRACT FROM AUTHOR]

The carbon chain ions HC 3 O + and HC 3 S + – longer variants of the famous 'X-ogen' line carrier HCO + – have been observed for the first time using two cryogenic 22-pole ion trap apparatus (FELion, Coltrap) and two different light sources: the Free Electron Laser for Infrared eXperiments (FELIX), which was operated between 460 and 2500 cm − 1 , and an optical parametric oscillator operating near 3200 cm − 1 ; signals from both experiments were detected by infrared predissociation action spectroscopy. The majority of vibrational fundamentals were observed for both ions and their wavenumbers compare very favourably with results from high-level anharmonic force field calculations performed here at the coupled-cluster singles and doubles level augmented by a perturbative treatment of triple excitations, CCSD(T). As the action scheme employed here probes the Ne-tagged weakly bound variants, Ne–HC 3 O + and Ne–HC 3 S + , corresponding calculations of these systems were also performed. Differences in the structures and molecular force fields between the bare ions and their Ne-tagged complexes are found to be very small. [ABSTRACT FROM AUTHOR]

The ground state of He–HCO+ is investigated using a recently developed double resonance technique, consisting of a rotational transition followed by a vibrational transition into a dissociative state. In order to derive precise predictions for the rotational states, the high resolution infrared predissociation spectroscopy of the v1 C–H stretching mode is revisited. Eleven pure rotational transitions are measured via the double resonance method. A least squares fit of these transitions to a standard linear rotor Hamiltonian reveals that the semirigid rotor model cannot fully describe the loosely bound He–HCO+ complex. The novel double resonance technique is compared with other action spectroscopic schemes, and some potential future applications are presented. [ABSTRACT FROM AUTHOR]

In the course of a 5 μm high-resolution infrared study of laser ablation products from carbon-sulfur targets, the ν1 vibrational mode region of linear C3S has been studied continuously from 2046 to 2065 cm−1. Besides the prominent vibrational fundamental, the region was found to feature the [ABSTRACT FROM AUTHOR]

A novel rotational spectroscopy method applicable to ions stored in cold traps is presented. In a double resonance scheme, rotational excitation is followed by vibrational excitation into a dissociative resonance. Its general applicability is demonstrated for the CH3+-He complex, which undergoes predissociation through its C-H stretching modes 1 and 3. High resolution rotational transitions are recorded for this symmetric top, and small unexpected splittings are resolved for K=1. Advantages and potential future applications of this new approach are discussed. [ABSTRACT FROM AUTHOR]

The carbon-rich molecular ions C 3 H＋ and HC 3 O＋ have been studied for the first time at high spectral resolution in the 5 μ m wavelength regime employing leak-out spectroscopy of their ν 2 (C 3 H＋) and ν 3 (HC 3 O＋) vibrational fundamentals. All measurements were performed in a newly built cryogenic 22-pole ion trap apparatus, the COLtrap II instrument. Besides the action spectroscopic characterization the new measurements have also been used towards optimization and an improved understanding of the leak-out process via a semi-quantitative kinetics model for which some rates are determined or estimated and rationalized. [Display omitted] • First rotationally resolved spectra of C 3 H＋ and HC 3 O＋ ions in the C-C stretching range. • Leak-out spectra measured in the new ion trap spectrometer COLtrap II. • Systematic studies optimizing the signal of leak-out spectroscopy • Kinetics model rationalizing the steps involved in the leak-out process [ABSTRACT FROM AUTHOR]

The carbon chain ions HC 3 O + and HC 3 S + – longer variants of the famous 'X-ogen' line carrier HCO + – have been observed for the first time using two cryogenic 22-pole ion trap apparatus (FELion, Coltrap) and two different light sources: the Free Electron Laser for Infrared eXperiments (FELIX), which was operated between 460 and 2500 cm − 1 , and an optical parametric oscillator operating near 3200 cm − 1 ; signals from both experiments were detected by infrared predissociation action spectroscopy. The majority of vibrational fundamentals were observed for both ions and their wavenumbers compare very favourably with results from high-level anharmonic force field calculations performed here at the coupled-cluster singles and doubles level augmented by a perturbative treatment of triple excitations, CCSD(T). As the action scheme employed here probes the Ne-tagged weakly bound variants, Ne–HC 3 O + and Ne–HC 3 S + , corresponding calculations of these systems were also performed. Differences in the structures and molecular force fields between the bare ions and their Ne-tagged complexes are found to be very small. [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]