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Two fundamental halocarbon ions, CH2Cl+ and CH3ClH+, were studied in the gas phase using the FELion 22-pole ion trap apparatus and the Free Electron Laser for Infrared eXperiments (FELIX) at Radboud University, Nijmegen (the Netherlands). The vibrational bands of a total of four isotopologs, CH235,37Cl+ and CH335,37ClH+, were observed in selected wavenumber regions between 500 and 2900 cm−1 and then spectroscopically assigned based on the results of anharmonic force field calculations performed at the CCSD(T) level of theory. As the infrared photodissociation spectroscopy scheme employed probes singly Ne-tagged weakly bound complexes, complementary quantum-chemical calculations of selected species were also performed. The impact of tagging on the vibrational spectra of CH2Cl+ and CH3ClH+ is found to be virtually negligible for most bands; for CH3ClH+–Ne, the observations suggest a proton-bound structural arrangement. The experimental band positions as well as the best estimate rotational molecular parameters given in this work provide a solid basis for future spectroscopic studies at high spectral resolutions. [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 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 low-frequency stretching and bending vibrations of the isotopologues CH 2 D + , CD 2 H + and CD 3 + have been recorded at low temperature and low resolution. For this, a cryogenic 22-pole trapping machine coupled to an IR beamline of the FELIX free electron laser facility has been used. To record the overview spectra, the laser induced reactions CD m H n + + H 2 → h ν CD m - 1 H n + 1 + + HD have been applied for these species. As this scheme is not applicable to CH 3 + , the latter has been tagged with He and subsequently dissociated by the IR beam. For the resulting CH 3 + - He spectrum, broad features are observed below 1000  cm - 1 possibly related to vibrational motions involving the He atom. The extracted vibrational band positions for all species are compared to results from high-level quantum-chemical calculations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cryogenic action spectroscopy is applied to protonated methyl cyanide, CH 3 CNH+, a potential interstellar molecule. • Broad-range vibrational gas-phase spectra are recorded with FELIX. • The extracted vibrational band positions allow to benchmark quantum-chemical calculations. • Discussion on the influence of rare-gas tagging on the vibrational band positions. • Prediction of rotational spectroscopic constants for low-lying vibrational states. The gas phase vibrational spectrum of CH 3 CNH+ is investigated using a messenger infrared predissociation (IRPD) action spectroscopic method. Vibrational bands were recorded in the 300-1700 cm−1 and 2000-3300 cm−1 regions making use of the widely tunable free electron laser for infrared experiments, FELIX, coupled to a cryogenic ion trap instrument. Band assignments were aided by high-level quantum-chemical calculations, which showed excellent agreement with the experimental data. Effects of the neon atom used as messenger in the IRPD method are investigated in detail. The data presented here will support astronomical searches for the CH 3 CNH+ ion in space, and provide a basis for high-resolution ro-vibrational and pure rotational studies in vibrationally excited states. [ABSTRACT FROM AUTHOR]

• Cryogenic action spectroscopy is applied to astrochemical relevant hydrocarbon ions. • Broadband vibrational gas-phase spectra of the propargyl and cyclopropenium cations are recorded with FELIX. • First spectroscopic characterization of their perdeuterated variants. • The extracted vibrational band positions allow to benchmark quantum-chemical calculations. • Isomer-selective formation pathways are investigated. Gas phase vibrational spectra of [C 3 H 3 ]+ isomers and their fully deuterated isotopologues measured in a cryogenic 22-pole ion trap are presented. The widely tunable free electron laser for infrared experiments, FELIX, was employed to cover the frequency range 500–2400 cm−1, complemented with an OPO/OPA system covering 2800–3400 cm−1. Spectral assignments for both the linear and cyclic isomeric form (H 2 C 3 H+ and c-C 3 H 3 +, respectively) are made based on various high-level computational studies. The effect of ion source conditions and different precursors (allene and propargyl chloride) for the preferential production of a specific isomer is discussed. The perturbation of the vibrational band position due to complexation with neon in the recorded infrared-predissociation (IRPD) spectra are also reported in this study. [ABSTRACT FROM AUTHOR]

[Display omitted] • Stable EI-MS molecular ions of Phenol and Aniline are the ground state structures. • Phenol and Aniline tautomers are not accessible with cryogenic ion trapping. • Phenol and Aniline deliver both cyclopentadiene [C 5 H 6 ] + radical cations. Molecular ions of phenol and aniline as well as the fragment ion at m / z 66 formed by electron ionization are examined with cryogenic messenger-IR ion spectroscopy and theory. According to the recorded IR spectra aromatic ground state molecular ions of phenol and aniline are clearly identified. Similar to earlier reports our new set of spectroscopic and computational results supports the assumption that tautomeric molecular ions of phenol and aniline are only short-lived intermediates in the reaction path to the ultimate CO loss reaction product of phenol as well as the HNC loss product of aniline. Even the present cryogenic messenger-IR ion spectroscopy approach failed to collect spectroscopic evidence of the intermediate presence of these elusive tautomers of phenol and aniline molecular ions. However, our study clearly shows that the electron ionization mass spectrometry dissociation product ion of phenol and aniline at m / z 66 is the cyclopentadiene radical cation [C 5 H 6 ] + for the presence of which convincing spectroscopic evidence could be collected proving the structure assignment and identification. All messenger-IR ion spectroscopy experiments were conducted on a cryogenic 22-pole ion trap with the use of neon atoms for tagging. The MS instrument was coupled to a free electron laser delivering wavelength tunable IR radiation for spectroscopy. Harmonic and anharmonic force field calculations complement the experiments and support band assignments of the recorded IR spectra and general data interpretation. [ABSTRACT FROM AUTHOR]