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Vinylsulfur pentafluoride (VSPF), a molecule with a four-fold internal rotor, —SF4, has been studied with high resolution Fourier transform microwave spectroscopy. We believe that this is the first report of resolved four-fold internal rotation. As such, we have presented the tools needed to understand and analyze such a problem. These include debugging the ERHAM computer program necessary to fit the spectra and the free rotor to high barrier correlation diagram necessary to understand the torsional states of the four-fold rotor. The A, E, and B torsional state rotational transitions are well resolved and assigned. Spectroscopic transitions of four isotopologues of VSPF, H2C=CH—SF5, the normal isotopologue, and the singly substituted 34S and 13C isotopologues were measured and assigned. Contrary to expectation, the A torsional state could not be fit with only a semi-rigid Hamiltonian. The barrier to internal rotation, V4, is found to be 227 cm−1. Ab initio calculations at the MP2 aug-cc-pVQZ level of theory and basis set were performed and the results of this calculation are compared to our experimental results. [ABSTRACT FROM AUTHOR]

Molecular pulsed jet, chirped-pulse Fourier transform microwave spectroscopy has been used to record 499 transitions for the title molecule. Measurements have been made in the 8–16 GHz regions. Vibrational and electronic ground state rotational constants A, B, and C have been obtained, together with centrifugal distortion terms. The complete iodine and nitrogen nuclear quadrupole coupling tensors have been determined for the first time. Quantum chemical calculations have been performed to aid with analyses and, in particular, to aid in determining the signs of the off-diagonal components of the nuclear quadrupole coupling tensors. An experimentally determined relative electronegativity scale for several polyhalomethyl groups is proposed. [ABSTRACT FROM AUTHOR]

Abstract: The pure rotational spectrum of 175Lu16O in its ground electronic state (X 2Σ+) has been observed with a cavity pulsed jet Fourier transform microwave spectrometer. The samples were prepared by laser ablation of Lu metal in the presence of gaseous oxygen, and stabilized in pulsed jets of Ar. The N =1–0 transition has been measured in the v = 0, 1 and 2 states. All the observed lines show Zeeman splittings caused chiefly by the Earth’s magnetic field. The transitions show effects of electron spin-rotation structure and of 175Lu hyperfine structure. Several hyperfine parameters have been evaluated, and are interpreted in terms of the molecular electronic structure. An improved equilibrium internuclear distance, r e, is presented. The results should facilitate astrophysical searches for the molecule. [Copyright &y& Elsevier]

The hydrofluoroether C4F9OCH3(methoxynonafluorobutane, HFE-7100) has been studied by chirped pulse Fourier transform microwave spectroscopy as vapor from the liquid participates in a supersonic expansion of argon. Two isomers are present, (CF3)2CFCF2OCH3and n-C4F9OCH3, and in each case the rotational spectra of only one, dominating, conformer has been assigned. Rotational constants, centrifugal distortion constants, and barriers to methyl group internal rotation for the observed species have been experimentally determined for the first time. We note that Ray’s asymmetry parameter for the (CF3)2CFCF2OCH3isomer is 0.007 083(1), indicating almost “perfect” asymmetry. Also, electronic structure calculations show an extremely short C(frame)−O ether bond length of 1.337 Å. [ABSTRACT FROM AUTHOR]

Abstract: A chirp Fourier transform microwave spectrometer has been used to record the rotational spectra of two isomers of the hydrofluoroether (ethoxynonafluorobutane also known as HFE-7200) between 7.8 and 16.2GHz. The target compound was spectroscopically examined as it participated in a supersonic expansion of argon. Four separate rotational spectra have been identified amongst the congested data. Spectroscopic parameters are presented for each species. The structures of all four species have been identified by exploring the multi-dimensional potential energy surfaces using quantum chemical calculations. [ABSTRACT FROM AUTHOR]

The pure rotational spectra of the two lowest energy conformers of 1,1,2,2-tetrafluoro-3-iodopropane have been investigated between the frequency limits of 7.5 and 16 GHz using chirped pulse Fourier transform microwave spectroscopy. Quantum chemical calculations have been performed to aid the spectral analyses. For the trans-trans conformer, which is calculated to be the lowest in energy, a total of 135 transitions were recorded. For the gauche-gauche conformer a total of 286 transitions were recorded. In both cases the complete iodine nuclear quadrupole coupling tensor has been determined. [ABSTRACT FROM AUTHOR]

XeAuF has been detected and characterized using microwave rotational spectroscopy. It was prepared by laser ablation of Au in the presence of Xe and SF6, and stabilized in a supersonic jet of Ar. The spectrum was measured with a cavity pulsed jet Fourier transform microwave spectrometer, in the frequency range 6-26 GHz. Rotational constants, centrifugal distortion constants, and 131Xe and 197Au nuclear quadrupole coupling constants have been evaluated. The molecule is linear, with a short XeAu bond (2.54 Å), and is rigid. The 131Xe nuclear quadrupole coupling constant (NQCC) is large (-135 MHz). The 197Au NQCC differs radically from that of uncomplexed AuF. The results are supported by those of ab initlo calculations which have given an XeAu dissociation energy ∼100 kJ mol-1, plus Mulliken and natural bond orbital populations, MOLDEN plots of valence orbitals, and an energy density distribution. All evidence is consistent with XeAu covalent bonding in XeAuF. [ABSTRACT FROM AUTHOR]

Abstract: Tin metal has been ablated with pulsed radiation from a Nd:YAG laser ( nm). Carbonyl sulfide, diluted in high pressure argon, has been pulsed into the resultant Sn plasma. One of the results of this experiment has been the production of SnS. These events have allowed a rotational spectrum of tin monosulfide to be studied using a chirped-pulse Fourier transform microwave spectrometer. The resolution of the spectrum obtained was sufficient to observe hyperfine structure from the 117Sn and 119Sn-containing SnS molecules. Tin nuclear spin-rotation hyperfine constants are reported for the first time. [Copyright &y& Elsevier]

The three lowest energy conformations of the title compound have been investigated using quantum chemical calculations and the lowest energy conformer has been observed using pure rotational spectroscopy. The lowest energy conformer possesses C 2 symmetry, a helical CF 2 backbone, with the hydrogens nearly eclipsing one another when looking down the long axis of the molecule. The technique of Fourier transform microwave spectroscopy in conjunction with quantum chemical calculations is demonstrated as a complimentary method to X-ray diffraction for structural determinations of small oligomers for which the location of hydrogen atoms may be important. [ABSTRACT FROM AUTHOR]

Abstract: The pure rotational spectrum of perfluorobutyryl fluoride, C3F7COF, was measured using a pulsed nozzle, chirped pulse Fourier transform microwave spectrometer. A total of 280 transitions for the only observed conformer were recorded and analyzed. The rotational constants are A =1397.4330(1)MHz, B =619.17456(8)MHz, and C =592.06831(8)MHz. Quantum chemical calculations and the spectral analysis indicate that the observed conformer is the skew–anti form with calculated dihedral angles CCCO=120°, and CCCC≈170°. Conformational differences between perfluorobutyryl fluoride, perfluorobutyryl chloride, butyryl fluoride and butyryl chloride are discussed. [Copyright &y& Elsevier]

The structure of 2H,3H-perfluoropentane, CF 3 CHFCHFCF 2 CF 3 , has been determine by a combination of Chirp-pulsed Fourier transform microwave (CP-FTMW) spectroscopy and cavity FTMW spectroscopy. Of the four possible stereoisomers, only the enantiomeric pair (R,R)/(S,S) were observed experimentally; there was no spectroscopic evidence for the enantiomeric pair (R,S)/(S,R). The conformeric structure of the (R,R)/(S,S) stereoisomer(s) was that of partial helices with C−C−C−C dihedral angles of 12° (helical) and 1° (staggered). [ABSTRACT FROM AUTHOR]

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]

The pure rotational spectra of 4,4,4-trifluorobutyric acid, CF 3 CH 2 CH 2 COOH, and its complex with formic acid were studied by a pulsed nozzle, chirped-pulse Fourier transform microwave spectrometer in the frequency range of 7–13 GHz. The rotational constants and centrifugal distortion constants were determined for the first time. Quantum chemical calculations were carried out exploring possible conformations of 4,4,4-trifluorobutyric acid and the structure of the 4,4,4-trifluorobutyric acid-formic acid complex using B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVTZ calculations. Only one conformer was observed for 4,4,4-trifluorobutyric acid and its complex with formic acid, in agreement with the calculations. [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 chirped pulse Fourier transform microwave spectrometer was used to obtain pure rotational spectra for CF3CF2Cl between 8GHz and 16GHz, and for CF3CF2Br between 8GHz and 14GHz. In both cases rotational constants, quartic centrifugal distortion constants and chlorine/bromine nuclear electric quadrupole coupling tensors were obtained for the first time. For both compounds only the trans conformer was observed. Quantum chemical calculations have provided structures with rotational constants closely matching the experimental values. For CF3CF2Br the spectra collected were sufficiently strong that the C-13 isotopologues could be observed in natural abundance. ΔJ =2 transitions were observed in the rotational spectrum of CF3CF2Br, but were not observed in the spectrum for CF3CF2Cl. [Copyright &y& Elsevier]

Abstract: The pure rotational spectrum of perfluoropropionic acid, CF3CF2COOH, has been studied by a pulsed nozzle, chirped-pulse Fourier transform microwave spectrometer in the frequency range of 8–14GHz. A total of 81 transitions, including a-type, b-type, and c-type transitions have been observed and analyzed. The rotational constants and the five quartic centrifugal distortion constants were determined for the first time. The rotational constants are A =1893.5299(4)MHz, B =1175.7031(4)MHz, and C =1118.2017(5)MHz. Quantum chemical calculations and the spectral analysis indicate that the observed conformer is the gauche form of perfluoropropionic acid with calculated dihedral angles CCCO=106° and 107° from MP2/6-311G++(3df, 3pd) and MP2/Aug-CC-pVDZ calculations, respectively. The experimental spectroscopic constants are compared to those obtained from ab initio calculations. [Copyright &y& Elsevier]

Propionyl chloride and perfluoropropionyl chloride have been characterized using chirped pulse Fourier transform microwave spectroscopy between the frequency range of 8 and 14 GHz. Molecules were studied in separate experiments in supersonic expansions of argon. The 35Cl, 37Cl, and each of the monoisotopic 13C substituted isotopologues of propionyl chloride were observed. The 35Cl and 37Cl isotopologues of perfluoropropionyl chloride were observed. Analyses of the resulting microwave spectra have yielded spectroscopic constants for the target molecules. The analyses indicate that, under the conditions of these experiments, both molecules are only detectable as cis conformers in which ∠CCCO = 0°. Comparisons are made between the electronic and geometric structure of propionyl chloride and perfluoropropionyl chloride, and also other acyl chlorides. The data produced are relevant in regards to quantifying the known destabilizing effect of perfluoroalky chains on carbonyl groups. Distinct differences in electronegativity between the CH3CH2CO− and CF3CF2CO− groups are discussed. Methyl group internal rotation is observed for propionyl chloride and has been analyzed to produce a V3barrier height. [ABSTRACT FROM AUTHOR]

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]

• Microwave spectra were recorded of the anti-anti and anti-gauche conformers of n -propyl nitrate. • Spectra of five isotopologues for each conformer have been assigned and fit. • The fit was made to a semi-rigid Hamiltonian including nuclear quadrupole hyperfine coupling. • r 0 and r s structural parameters have been determined from the data. The rotational spectrum of n -propyl nitrate was measured in the frequency range between 6 and 18 GHz using a Balle-Flygare Fourier transform microwave jet/cavity spectrometer. Parent, 13C and 15N isotopologue transitions for the lower-energy anti-gauche (AG) conformer were found using this instrument. The search for spectra from other conformers was performed using a broadband chirped-pulse jet spectrometer. Transitions from the anti-anti (AA) conformer were observed in this manner. Parent, 13C and 15N isotopologue transitions for the AA conformer were rescanned using the cavity instrument to improve resolution and the signal-to-noise ratio. Rotational, centrifugal distortion, and nuclear electric quadrupole coupling constants for all conformers/isotopologues were fit using Pickett's SPFIT program. The structure of n -propyl nitrate is discussed considering these results. [ABSTRACT FROM AUTHOR]

• A new E-band chirped pulse Fourier transform spectrometer is described in detail. • The performance of the spectrometer is characterized. • The pressure broadening of transitions of OCS in He are fit to a time domain Voigt model. • These results are compared to previous work and applications towards collecting spectra in high pressure environments are discussed. Product channel-specific reaction kinetics at low temperature presents a significant challenge for both experiment and theory but provides essential inputs for astrochemical models of cold interstellar environments. Reaction kinetics studies using chirped pulse Fourier transform microwave (CP-FTMW) spectroscopy provide a potential solution but require the use of a buffer gas to thermalize the reactants and products; however, collisions with the buffer gas reduce the length of the detected signal, the free induction decay, through pressure broadening. The effect of this on time domain signals is largely unexplored using CP-FTMW spectrometers. A new E-band (60–90 GHz) spectrometer has been constructed using previously unavailable equipment in order to maximize its performance for detecting molecules in collisional environments. The design of this spectrometer is described in detail. The pressure broadening of OCS in He was used to test the spectrometer under collisional conditions similar to those that are routinely used to perform reaction kinetics measurements. The corresponding pressure broadening coefficients for transitions in this frequency range were determined at room temperature and the performance of the spectrometer was assessed in relation to recently reported chirped pulse in uniform flow experiments. [ABSTRACT FROM AUTHOR]