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Abstract: Using pulsed jet chirped-pulse, and cavity-based Fourier transform microwave spectroscopies over 900 transitions have been recorded for the title molecule in the 1–4GHz and 8–18GHz regions. The and carbon-13 species have been observed in natural abundance allowing a substitution structure for the CCC backbone to be determined. Nearly all the transitions observed were either a-type R branches or b-type Q branches. No c-type transitions were observed consistent with only the trans conformer being present under our experimental conditions. The and components of the iodine nuclear quadrupole coupling tensor have been determined. Of note, several forbidden, transitions, and one transition were observed with quite reasonable intensity. These observations have been rationalized through considerations of near degeneracies between energy levels connected via a large value (≈1GHz). [Copyright &y& Elsevier]

Graphical abstract Highlights • Rotational spectra of 2-bromopyridine. • Measurement of the electric nuclear quadrupole coupling (NQC) tensors of 79Br, 81Br, and 14N. • Investigation of these NQC tensors by the use of the Extended Townes-Dailey analysis. Abstract The rotational spectrum of 2-bromopyridine was reinvestigated in the frequency range of 10–15.5 GHz by Fourier transform microwave (FTMW) spectroscopy. New observations of 14N hyperfine splittings have been observed for both the bromine-79 and -81 isotopologues in addition to five centrifugal distortion constants. Rotational constants and bromine nuclear quadrupole coupling tensors have been refined. Both the bromine and the nitrogen nuclear quadrupole coupling tensors have been investigated using the Extended Townes-Dailey analysis. [ABSTRACT FROM AUTHOR]

The first microwave study of 1-iodobutane, performed by Steinmetz et al. in 1977, led to the determination of the B + C parameter for the anti-anti- and gauche-anti-conformers. Nearly 40 years later, this reinvestigation of 1-iodobutane, by high-resolution microwave spectroscopy, led to the determination of rotational constants, centrifugal distortion constants, nuclear quadrupole coupling constants (NQCCs), and nuclear-spin rotation constants belonging to both of the two previously mentioned conformers, in addition to the gauche-gauche-conformer, which was observed in this frequency regime for the first time. Comparisons between the three conformers of 1-iodobutane and other iodo- and bromoalkanes are made, specifically through an analysis of the nuclear quadrupole coupling constants belonging to the iodine and bromine atoms in the respective chemical environments. [ABSTRACT FROM AUTHOR]

The pure rotational spectrum of a Claisen rearrangement precursor, Allyl Phenyl Ether (APE), has been measured on a chirped pulse Fourier transform microwave (CP-FTMW) spectrometer in the 8–14 GHz region. Rotational and centrifugal distortion constants for multiple conformations have been determined and are reported for the first time. This is the first study of a phenyl-containing ether where multiple conformers were experimentally observed all within their ground vibrational states. Quantum chemical calculations have been performed to isolate low energy geometries of APE and are implemented to aid in spectral assignment. Other structural parameters such as planar moments and inertial defects for the Allyl Phenyl Ether conformers are presented and compared to similar molecules. [ABSTRACT FROM AUTHOR]

[Display omitted] • Questioning the planarity of the open shell difluorocyanomethyl radical. • Complex hyperfine structures observed in the microwave spectrum. • Spin-rotation coupling, nuclear quadrupole coupling, and Fermi contact interactions. The pure rotational spectrum of the open shell difluorocyanomethyl radical, ĊF 2 CN, has been measured using two Balle-Flygare-type cavity Fourier-Transform-Microwave (FTMW) spectrometers both equipped with pulsed discharge nozzles. A total of 156 transitions (from N = 1 – 0 to 6 – 5, and K a = 0, 1, 2, 3) in the electronic ground state were observed between 6.5 GHz and 38.4 GHz with a typical linewidth of ∼5 kHz full-width-half-maximum. A Hamiltonian that included semi-rigid rotor, spin-rotation, and nuclear hyperfine parameters was fit to the observed data set and these parameters have been interpreted and compared to similar radicals. Excellent agreement between experimental and uB3LYP/aug-cc-pVQZ calculated rotational constants, the experimental inertial defect, −0.6858(2) uÅ2, and the failure of a coupling scheme in which the fluorine nuclei are treated as identical and related by a C 2v symmetry axis combine to indicate a nonplanar structure for the ĊF 2 CN radical. [ABSTRACT FROM AUTHOR]

Abstract: The pure rotational spectrum of tin monochloride, SnCl, has been measured and analyzed using chirped pulse and cavity Fourier transform microwave spectrometers equipped with a laser ablation source. SnCl, in its electronic state, has been measured in the 8–17GHz region. Rotational constants, centrifugal distortion constants, Λ-doubling constants, magnetic hyperfine constants, and nuclear electric quadrupole coupling constants for multiple isotopologues have been determined and are reported. The bond length, nuclear magnetic and quadrupole constants have been analyzed and compared against the family of tetral halides. Analysis of the bond length and hyperfine interactions point to a Sn–Cl single bond which is largely ionic in nature. [Copyright &y& Elsevier]

Abstract: A potential energy scan of chlorodifluoroacetyl chloride, ph name="dbnd" />O)Cl, at the MP2/6-311+G(d) level of theory predicts stable gauche and trans conformers, with . Ab initio calculations were made of approximate equilibrium structures of these and, on these structures, calculations were made of 35Cl and 37Cl nuclear quadrupole coupling constant tensors. Coupling constants here predicted, as well as rotational constants and molecular dipole moments, are applied to aid analyses of experimental microwave spectra. Chirped pulse Fourier transform microwave spectroscopy has been used to rapidly record the rotational spectra of four isotopologues of the title molecule, , namely 35Cl 35Cl, 35Cl 37Cl, 37Cl 35Cl, and 37Cl 37Cl. Only the gauche conformer was observed under the experimental conditions. For the four isotopologues a total of 464, 219, 197, and 77 transitions have been recorded, respectively. With the exception of the 37Cl 37Cl isotopologue sufficient data was available to determine all Cl quadrupole coupling tensors. Comparisons between the theoretical and experimental results are made. [ABSTRACT FROM AUTHOR]

Abstract: Pulsed jet chirped-pulse Fourier transform microwave spectroscopy has been used to record 264 transitions for the 79-Br species and 239 transitions for the 81-Br species of the title molecule. Measurements have been made in the 8–14GHz regions. The complete 79-Br, 81-Br and N quadrupole coupling tensors have been determined for the first time. [Copyright &y& Elsevier]

Abstract: A Fourier transform microwave spectrometer has been used to make high resolution measurements on the J =1–0 rotational transition for 11 isotopomers of SnO. For the most abundant isotopomer the transition was observed in the v =0,1,2,and 3 states. Magnetic hyperfine structure was observed in the transitions for 115Sn16O, 117Sn16O and 119Sn16O. The nuclear spin-rotation constant C I (Sn) has been determined for these isotopomers for the first time and these constants have been related to nmr shielding parameters. A multi-isotopomer analysis, including data from the 120Sn17O and 120Sn18O isotopomers, has been performed on the data. Born–Oppenheimer breakdown parameters were required in the fit and these parameters have been compared to those for the other Sn-chalcogenides. [Copyright &y& Elsevier]

Abstract: Two aluminum mirrors with radii of 203.2mm and radii of curvature also of 203.2mm have been used to construct a tunable Fabry–Perót type resonator with Q values of ∼200 at frequencies as low as 500MHz. The resonator has been incorporated into a pulsed nozzle, Fourier transform, Balle–Flygare spectrometer typically used for recording pure rotational spectra in the microwave region. The resonator design allows the instrument to access the radio frequency region (⩽3GHz) of the electromagnetic spectrum. The spectrometer is of use in (i) recording low J transitions of large asymmetric molecules where the spectra are often greatly simplified compared to higher frequency regions; (ii) measuring hyperfine constants for heavy molecules with higher accuracy than may be obtained at higher frequencies where hyperfine structure may not be resolvable; and (iii) provides further synchronicity between laboratory based measurements and radio astronomy in the 30cm region. The resonators use is illustrated by recording the rotational spectra of bromobenzene and iodobenzene. The lowest ΔJ =+1 transition for iodobenzene has been observed at 1130.5292(10)MHz. [Copyright &y& Elsevier]