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The pure rotational spectra of 18 and 21 isotopic species of GeSe and GeTe have been measured in the frequency range 5-24 GHz using a Fabry-Pérot-type resonator pulsed-jet Fourier-transform microwave spectrometer. Gaseous samples of both chalcogenides were prepared by a combined dc discharge/laser ablation technique and stabilized in supersonic jets of Ne. Global multi-isotopologue analyses of the derived rotational data, together with literature high-resolution infrared data, produced very precise Dunham parameters, as well as rotational constant Born-Oppenheimer breakdown (BOB) coefficients (δ01) for Ge, Se, and Te. A direct fit of the same datasets to an appropriate radial Hamiltonian yielded analytic potential-energy functions and BOB radial functions for the X1Σ+ electronic state of both GeSe and GeTe. Additionally, the electric quadrupole and magnetic hyperfine interactions produced by the nuclei 73Ge, 77Se, and 125Te were observed, yielding much improved quadrupole coupling constants and first determinations of the spin-rotation parameters. [ABSTRACT FROM AUTHOR]

The cm-wave rotational spectrum of 4-cyanopyridine was studied on a pulsed supersonic jet-expansion Fourier-transform microwave spectrometer. The ground state rotational parameters for the parent and four 13C and two 15N isotopologues were determined with high accuracy in natural abundance including all quartic centrifugal distortion constants and nuclear quadrupole coupling parameters of the two nitrogen nuclei. With the study of both singly substituted 15N species, the nuclear origins of the hyperfine structures could be differentiated and the respective constants identified unambiguously. Different approaches have been used to determine the structure: empirical (rs), ab initio and semi-experimental () methods. The semi-experimental approach improves the accuracy significantly, whereas the Kraitchman's method fails again. [ABSTRACT FROM AUTHOR]

The rotational spectra of four isotopologues of the 1:1 complex between chloromethane and water revealed the presence of only one rotamer in a pulsed jet expansion. The two subunits are linked through two weak hydrogen bonds, OH⋅⋅⋅Cl ( RH⋅⋅⋅Cl=2.638(2) Å) and CH⋅⋅⋅O ( RH⋅⋅⋅O=2.501(2) Å), forming a five-membered ring. All transitions display the hyperfine structure due to the 35Cl (or 37Cl) nuclear quadrupole effects. Dynamical features in the spectrum are caused by two large-amplitude motions. Each component line appears as an asymmetric doublet with a relative intensity ratio of 1:3. The splittings led to the determination of barrier to internal rotation of water around its symmetry axis, V2=320(10) cm−1. Finally, an unexpected small value of the inertial defect (−0.96 uÅ2 rather than −3.22 uÅ2) allowed the estimation of the barrier to the internal rotation of the CH3 group, V3≈8 cm−1. [ABSTRACT FROM AUTHOR]

Highlights: [•] Combined analysis of optical and microwave transitions. [•] Identification of 171YbF low-rotational branch features. [•] Precise determination of 171Yb magnetic hyperfine parameters. [Copyright &y& Elsevier]

Abstract: The rotational spectrum of the symmetric top trimethyl tin chloride (CH3)3SnCl has been studied using a pulsed molecular beam Fourier transform microwave spectrometer in the frequency range from 3 to 24GHz. The spectrum is exceedingly complicated by the internal rotation motions of the three equivalent methyl tops, the high number of Sn- and Cl-isotopes and the quadrupole hyperfine structure of the chlorine nucleus. In this paper, we present the microwave spectrum, ab initio calculations, permutation inversion (PI) group-theoretical considerations, Stark-effect measurements and finally the K =0 assignments and fits of the different torsion–rotation species. Based on the Stark-effect measurements, the dipole moment is μ =3.4980(30)D. Due to -mixing effects we observe linear Stark-effect behavior and additional quadrupole splitting for some torsion–rotation transitions in (CH3)3SnCl, which can be group-theoretically explained. The symmetric rotor fit of and A 2 torsion-rotation states leads to an effective B-constant of 1680.040124(92)MHz for the main isotopologue (CH3)3 120Sn35Cl. A global fit of 182 torsion–rotation transitions yields a torsional barrier of 1.774(6)kJ. [Copyright &y& Elsevier]

The microwave rotational spectrum of the aromatic 2,3-difluorophenol (2,3-DFP) has been recorded and analyzed in the frequency range of 5–25 GHz using a pulsed-jet Fourier transform microwave spectrometer. Rotational transitions were measured for the parent, the 18O, and all six 13C singly substituted isotopologues in natural abundance as well as the deuterium enriched 2HO-species. In addition to the rotational and quartic centrifugal distortion parameters, the quadrupole coupling constants of the deuterium species were determined. The rotational constants for the parent species are obtained as A = 2313.37516(14) MHz, B = 1797.935693(62) MHz, C = 1011.695171(36) MHz. For the deuterated species, the 2H quadrupole coupling constants are χ aa = −0.11693(80) MHz and (χ bb − χ cc) = 0.4112(14) MHz. The partial r s substitution structure as well as a semi-experimental r 0 structure was determined from the rotational constants of the observed isotopologues. Both r s and r 0 structures agree well with each other and with MP2/6-311++g(2d, 2p) and B3LYP/6-311++g(2d, 2p) predicted equilibrium structures with the biggest deviation in heavy atom bond lengths being 0.008 Å. The microwave spectrum of 2,3-difluorophenol shows a single conformer forming an OH⋯F internal hydrogen bridge. The rotational transitions of the deuterated isotopologue, C 6 H 3 F 2 OD, exhibit resolved 2H nuclear quadrupole hyperfine structure. Image 1 • Supersonic Jet Cooled Rotational Spectrum of 2,3-difluorophenol has been studied. • The ground-state rotational parameters for the parent and eight isotopic species were determined with high accuracy. • Deuterium nuclear quadrupole hyperfine constants were determined for the D isotopologue. • Substitution structure of the molecule has been determined. • Experimental study is substantiated with ab initio and density functional calculations. [ABSTRACT FROM AUTHOR]

Abstract: Rotational transitions of iso-propyl cyanide, (CH3)2CHCN, also known as iso-butyronitrile, were recorded using long-path absorption spectroscopy in selected regions between 37 and 600GHz. Further measurements were carried out between 6 and 20GHz employing Fourier transform microwave (FTMW) spectroscopy on a pulsed molecular supersonic jet. The observed transitions reach J and K a quantum numbers of 103 and 59, respectively, and yield accurate rotational constants as well as distortion parameters up to eighth order. The 14N nuclear hyperfine splitting was resolved in particular by FTMW spectroscopy yielding spin–rotation parameters as well as very accurate quadrupole coupling terms. In addition, Stark effect measurements were carried out in the microwave region to obtain a largely revised c-dipole moment component and to improve the a-component. The hyperfine coupling and dipole moment values are compared with values for related molecules both from experiment and from quantum chemical calculations. [Copyright &y& Elsevier]

Abstract: Cyanoacetylene enriched in deuterium was used to record pure rotational transitions of DC3N and its rare 13C and 15N isotopic species by employing Fourier transform microwave (FTMW) spectroscopy on a supersonic-jet expansion at centimeter wavelengths (8.2–25.4GHz) and by using long-path absorption spectroscopy at millimeter and submillimeter wavelengths (82–900GHz). In addition, submillimeter wave measurements (304–897GHz) have been performed for DC3N in its lowest excited vibrational state. Hyperfine structure caused by the 14N and D nuclei has been resolved in the FTMW spectra. Quantum-chemical calculations have been performed on the hyperfine structure parameters at the coupled-cluster level (CCSD(T)) with up to core-polarized quintuple zeta basis-sets and were found to be in excellent agreement with experimental data as far as these were available. Vibrational corrections on the quadrupole coupling parameters have been evaluated at the MP2 level employing a quadruple zeta basis-set. The present and previous data were fit simultaneously to obtain accurate predictions for the identification of these species in space. [Copyright &y& Elsevier]

• First reported rotational spectrum of the C 2 F 4 S 2 ⋯NH 3 complex. • First extended Townes-Dailey analysis of an ammonia complex. • Chalcogen bonding interaction. Six isotopologues of the 2,2,4,4-tetrafluoro-1,3-dithietane⋯ammonia complex were characterized by rotational spectroscopy. Accurate molecular structures of the observed dimer were obtained combining quantum chemical calculations and experimental results employing Kraitchman's equations. To further investigate the non-covalent interactions between the two subunits, the nuclear quadrupole hyperfine structure was analyzed and interpreted. Additionally, natural bond orbital and non-covalent interactions analyses were applied. A N⋯S σ-hole interaction characterizes the structure of the observed complex. [ABSTRACT FROM AUTHOR]

Rotational transitions of the only conformer of 4-chlorophenol and the two conformers of 3-chlorophenol (syn and anti) were measured in the frequency range of 10.5–21.0 GHz using broadband pulsed-jet Fourier transform microwave spectroscopy. For the two conformers of 3-chlorophenol, the complete nuclear quadrupole coupling tensors of chlorine, χ, were obtained. Rotational, centrifugal distortion and quadrupole coupling constants were determined for each conformational species, comprising the 35Cl and 37Cl isotopologues. An extended Townes-Dailey analysis was performed on the obtained quadrupole coupling tensors and the results are discussed regarding the effects of different functional groups at different substitution positions of the benzene ring. Together with reanalyzed literature data, this analysis supplements established concepts in organic chemistry to predict and explain the reactivity of aromatic molecules. Probing Resonance E_ects in Aromatic Systems by Nuclear Quadrupole Coupling: Investigations of 3- and 4-Chlorophenol by Rotational Spectroscopy Philipp Buschmann, Kevin G. Lengsfeld, Sven Herbers, Stefanie Genuit, Cara M. H ohne, Jens-Uwe Grabow Image 1 • First rotational spectroscopy characterization of two conformers of 3-chlorophenol. • First completely analyzed quadrupole hyperfine structure of 4-chlorophenol. • Extended Townes-Dailey analyses of all investigated species. • First comparison of chlorinated aromatic molecules by extended Townes-Dailey approach. • Conclusions drawn on reactivity by evaluating substitution effects. [ABSTRACT FROM AUTHOR]

• First reported high resolution microwave spectrum of acetone cyanohydrin. • First characterization of Coriolis coupling and hyperfine structure. • Spectral complexity due to large amplitude motions. Rotational transitions of gauche -acetone cyanohydrin are measured in the microwave range between 5 and 23 GHz. Results from quantum chemical calculations indicate that the hydrogen atom of the hydroxyl group undergoes a tunneling motion connecting two equivalent structures. The observed signals are assigned to the two lowest tunneling substates 0 + and 0 - , which belong to either a - or c -type transitions exhibiting Coriolis splittings of a few MHz. Additional hyperfine structure arises from the quadrupole coupling 14N nucleus. The energy separation Δ E between the 0 + and 0 - states is predicted to be around 50 GHz. The molecular structure and internal dynamics are discussed in terms of their spectral signatures. [ABSTRACT FROM AUTHOR]

• Highly accurate microwave frequencies obtained for HC 5 N. • Improved spectroscopic parameters to facilitate radio astronomical observations. • First determination of 14N spin-rotation parameter and improved quadrupole value. • Some improvement achieved for HC 7 N. • Quantum chemical calculations on hyperfine parameters of HCN to HC 7 N. Very accurate transition frequencies of HC 5 N were determined between 5.3 and 21.4 GHz with a Fourier transform microwave spectrometer. The molecules were generated by passing a mixture of HC 3 N and C 2 H 2 highly diluted in neon through a discharge valve followed by supersonic expansion into the Fabry-Perot cavity of the spectrometer. The accuracies of the data permitted us to improve the experimental 14 N nuclear quadrupole coupling parameter considerably and the first experimental determination of the 14 N nuclear spin-rotation parameter. The transition frequencies are also well suited to determine in astronomical observations the local speed of rest velocities in molecular clouds with high fidelity. The same setup was used to study HC 7 N, albeit with modest improvement of the experimental 14 N nuclear quadrupole coupling parameter. Quantum chemical calculations were carried out to determine 14 N nuclear quadrupole and spin-rotation coupling parameters of HC 5 N, HC 7 N, and related molecules. These calculations included evaluation of vibrational and relativistic corrections to the non-relativistic equilibrium quadrupole coupling parameters; their considerations improved the agreement between calculated and experimental values substantially. [ABSTRACT FROM AUTHOR]