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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]

Results of large-scale coupled-cluster calculations of selected C2H2Si and CNHSi structural isomers are reported. Equilibrium molecular structures of a total of 12 molecules in their singlet electronic states have been calculated systematically employing the coupled-cluster singles and doubles model augmented by a perturbative correction for triple excitations (CCSD(T)) in combination with Dunning’s hierarchy of correlation consistent basis sets. In addition, anharmonic force fields were calculated to yield fundamental vibrational frequencies and rotation-vibration interaction constants αiA,B,C. The latter were used to determine empirical equilibrium structures reemp of two molecules — silacyclopropenylidene, c-C2H2Si, and silapropadienylidene, H2CCSi — for which sufficient isotopic data are available from literature. Very good agreement with theoretical equilibrium structures from CCSD(T) calculations employing core-valence basis sets of quadruple and quintuple-zeta quality — i.e., cc-pwCVQZ (337 basis functions), cc-pCV5Z, and cc-pwCV5Z (581 basis functions) is found — to within 0.001 Å for bond lengths and 0.1° for bond angles. Theoretical ground state rotational constants of HSiCN and HSiNC compare very favorably with experimental microwave data from literature, to within 0.15% (HSiCN) and 0.1% (HSiNC) for the B0 and C0 rotational constants. In the case of c-C2H2Si and H2CCSi this agreement is even better than 0.1%. For the latter two molecules effects of higher-level electron-correlation and relativity to the equilibrium geometry as well as the electronic contributions to the rotational constants are investigated. For eight molecules not yet studied at high spectral resolution in the gas-phase theoretical molecular parameters are provided to support future laboratory investigations. Theoretical vibrational fundamentals compare well with data of eight species studied previously with infrared matrix isolation spectroscopy. [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]

The low-lying rotational states ( J = 0, … , 5) of CD 2 H + have been probed by high-resolution ro-vibrational and pure rotational spectroscopy, applying several action spectroscopic methods in a cryogenic 22-pole ion trap. For this, the ν 1 ro-vibrational band has been revisited, detecting 108 transitions, among which 36 are new. The use of a frequency comb system allowed us to measure the ro-vibrational transitions with high precision and accuracy, typically better than 1 MHz. The high precision has been confirmed by comparing equal combination differences in the ground and excited state. Moreover, precise predictions of pure rotational transitions were possible for the ground state. Twenty-five rotational transitions have been detected directly by a novel IR-mm-wave double resonance method, giving rise to highly accurate ground state spectroscopic parameters. [ABSTRACT FROM AUTHOR]

The vibrational transitions and the relative abundances of the two isomeric ions H 2 CNH+ and H 2 NCH+ generated through electron impact ionisation have been investigated in a noble gas tagging experiment. It could be shown that both species were formed with an abundance of 70 and 30% for H 2 NCH+ and H 2 CNH+, respectively. The obtained vibrational bands of the two species have been assigned to vibrational transitions through comparison with the results of ab initio calculations. These computations also predict both species to be moderately polar. The present investigations show that both isomers should be included in chemical model calculations of dark interstellar clouds, protoplanetary disks, star-forming regions as well as planetary atmospheres. [Display omitted] • Overview: This paper presents a spectroscopic study of H 2 CNH+ and its isomer, the aminomethylene cation. • Core findings: The vibrational transitions and the relative abundances of the two isomeric ions of H 2 CNH+ and H 2 CNH+. • Significance: Our study shows that both isomers should be included in astrochemical models. [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]

Isothermal surfaces within the device [Display omitted] • First high-resolution far-infrared study of vinyl acetylene. • Two energetically lowest vibrational fundamentals and their hotbands studied. • Millimeter-wave vibrational satellites reported for the first time. • Global fits of infrared and pure rotational spectra performed. The high resolution vibrational spectrum of vinyl acetylene (C 2 H 3 CCH) has been investigated in the far infrared region from 180 to 360 cm−1 using the Bruker IFS 120 HR spectrometer at Justus-Liebig-Universität, Gießen, Germany. The two energetically lowest vibrational fundamentals ν 13 and ν 18 at 214 cm−1 and 304 cm−1, respectively, were measured at a resolution of 0.0016 cm−1. In addition to the fundamental modes, several hot bands originating from either ν 13 or ν 18 were observed and analyzed. The spectroscopic analysis was supported by high-level quantum-chemical coupled-cluster calculations and also made use of the Automated Spectral Line Assignment Procedure, ASAP, outlined earlier (Martin-Drumel et al., 2015). In addition to the infrared study, so far unpublished millimeter-wave vibrational satellites that were measured in the course of an earlier study of the pure rotational spectrum of vinyl acetylene in its ground vibrational state (Thorwirth and Lichau, 2003) were added to the data set and are reported here for the first time. [ABSTRACT FROM AUTHOR]

[Display omitted] • First spectroscopic study of a polyatomic carbon-selenium species. • The ν 3 mode of SeCCCSe has been investigated at high spectral resolution. • Six isotopic species were detected providing structural information. • The experimental study was complemented by high-level CCSD(T) calculations. High-resolution infrared studies of laser ablation products from carbon-selenium targets have revealed a new vibrational band at 2057 cm−1 that is identified as the ν 3 vibrational fundamental of the SeC 3 Se cluster. Because of the rich isotopic composition of selenium and the heavy nuclear masses involved, the vibrational band shows a relatively compact and complex structure despite the simple linear geometric arrangement. Overall, rotational-vibrational lines of six isotopologues could be assigned and fitted permitting the derivation of an accurate selenium-carbon bond length. Spectroscopic analysis has been greatly supported by high-level quantum-chemical calculations of the molecular structure and the harmonic and anharmonic force fields performed at the CCSD(T) level of theory. Scalar-relativistic effects on the molecular structure were also considered but found of little importance. [ABSTRACT FROM AUTHOR]

• First high-resolution infrared study of ethyl cyanid. • Four energetically lowest vibrational fundamentals studied. • Global fits of infrared and pure rotational spectra performed. • Strong vibrational satellites towards high mass star forming region assigned. The high resolution vibrational spectrum of ethyl cyanide (C 2 H 5 CN) has been investigated in the far-IR using synchrotron-based Fourier transform spectroscopy. The assignment was performed using the Automated Spectral Assignment Procedure (ASAP) allowing accurate rotational energy levels of the four lowest fundamental vibrations of the species, namely the v 13 = 1 @ 205.934099(8) cm−1, v 21 = 1 @ 212.141101(8) cm−1, v 20 = 1 @ 372.635293(15) cm−1, and v 12 = 1 @ 532.699617(16) cm−1 states, to be determined. The analysis not only confirms the applicability of the ASAP in the treatment of (dense) high-resolution infrared spectra but also reveals some of its limitations. Complementary to the infrared study, the pure rotational spectrum of C 2 H 5 CN was also studied in selected frequency ranges from 75 to 255 GHz. New observations of a prototypical high-mass star-forming region, G327.3–0.6, performed with the Atacama Large Millimeter Array show that vibrational satellites of C 2 H 5 CN can be very intense, of order several tens of Kelvin in units of brightness temperature. [ABSTRACT FROM AUTHOR]