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Abstract: The pure rotational spectrum of 2,2-bis(trifluoromethyl)oxirane has been recorded using a chirped pulse Fourier transform microwave spectrometer. A total of 317 transitions have been recorded and spectroscopic constants have been determined for the first time. Quantum chemical calculations suggest that at equilibrium the two CF3-groups have a slightly staggered configuration with respect to one another. However, the barrier to an eclipsed configuration is calculated to be very low, ≈10cm−1. Arguments are presented suggesting that the zero-point energy of the molecule is above the barrier to the CF3 eclipsed structure such that the zero-point geometry can reasonably be described as possessing eclipsed CF3-groups. [Copyright &y& Elsevier]

Abstract: A chirped pulse Fourier transform microwave spectrometer has been used to record the pure rotational spectrum of perfluorobutyryl chloride seeded in a pulsed supersonic expansion of argon gas. Only one conformer of the title molecule was observed. For the 35Cl species a total of 236 spectral transitions were recorded. Quantum chemical calculations together with the spectral constants obtained indicate that the observed conformer has the CCCCOCl centers contained within the ab plane with a dihedral angle ∠CCCO=0°. [Copyright &y& Elsevier]

The pure rotational spectrum of the X1Σ+ ground electronic state of platinum monosilicide has been measured for nine isotopomers. For the most abundant isotopomer, 194Pt28Si, the J=1–0 and the J=2–1 transitions were recorded up to the fourth vibrationally excited state. The data set obtained enabled a multi-isotopomer fit to a Dunham-type expression and the constants Y01, Y02, Y11, Y21, and Y31 were determined. In the process of fitting the data it was necessary to include Born–Oppenheimer breakdown correction terms and the values and significance of these terms are discussed. Strong evidence is presented indicating within the rotational spectrum the presence of field shift effects due to the finite size of the Pt nucleus. The nuclear spin–rotation constant, CI(195Pt) is found to be 30.98(157) kHz in the ground vibrational state. Hyperfine structure arising from the 29Si nucleus was not observed. The measurement of Stark shifts in the rotational spectrum of PtSi has enabled the determination of the dipole moments for the 194Pt28Si and 196Pt28Si isotopomers. [Copyright &y& Elsevier]

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]

Abstract: An experimental study has been performed shedding light on the conformational energies of the asymmetric ether n-butyl ethyl ether. Rotational spectroscopy between 7.8GHz and 16.2GHz has identified two conformers of n-butyl ethyl ether, C4H9OC2H5. In these experiments spectra were observed as the target compound participated in an argon expansion from high to low pressure causing molecular rotational temperatures to be below 4K. For one conformer, 95 pure rotational transitions have been recorded, for the second conformer, 20 pure rotational transitions were recorded. Rotational constants and centrifugal distortion constants are presented for both butyl ethyl ether conformers. The structures of both conformers have been identified by exploring the multi-dimensional molecular potential energy surface using ab initio calculations. From the numerous low energy conformers identified using ab initio methods, the three lowest conformers were pursued at increasingly higher levels of theory, i.e. complete basis set extrapolations, coupled cluster methods, and also taking into consideration zero point vibrational energies. The two conformers observed experimentally are only revealed to be the two lowest energy conformers when high levels of quantum chemical methodologies are employed. [Copyright &y& Elsevier]

Abstract: The pure rotational spectrum of CHF2I has been recorded for the first time, in a supersonic expansion in the region 1.7–17GHz, and at room-temperature in the region 302–318GHz. The observed transitions span the values of from 0 up to 67. Precise rotational and centrifugal distortion constants have been determined. Furthermore, the complete iodine nuclear electric quadrupole coupling tensor, in the inertial and principal axes, has been determined. Quantum chemical calculations have been performed to aid with the analysis. Iodine quadrupole mediated perturbations have resulted in the following observations: (i) several transitions having enhanced intensities and (ii) the observation of several forbidden, , transitions. Comparisons in electronic structure are made between the series of molecules ; and X=Cl, Br, I. [Copyright &y& Elsevier]

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 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]

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: New molecular structural data is presented for a cyanide terminated oligomer of polytetrafluoroethene. The target molecule, CF3–(CF2)6–CN, has been seeded within a pulsed supersonic expansion of argon. The result of this action is to cool the species to rotational temperatures below 4K. Within this state, the pure rotational spectrum of the oligomer has been recorded using two types of Fourier transform microwave spectroscopy. A total of 111 transitions have been identified involving rotational J levels between 6 and 40. Only a- and b-type transitions were observed. The spectrum has been analyzed using a Hamiltonian containing all three rotational constants and one centrifugal distortion constant, D J . The experimental spectroscopic constants have been used to develop an effective molecular structure by scaling the quantum chemical calculated structure. The data shows that the seven carbon perfluorinated chain for the isolated oligomer twists ≈104°. This compares well to the C7F13-twist of ≈97° anticipated from the X-ray structure of phase II polytetrafluoroethene. [Copyright &y& Elsevier]

Abstract: The first far-infrared high resolution absorption measurement of the cis-methyl nitrite molecule has been recorded in the range 15–400cm−1 using the synchrotron AILES beamline radiation at SOLEIL with a resolution of 0.0011cm−1. First assignments for the pure rotational transitions (15–65cm−1) belonging to the ground νt (=ν 15)=0 and first νt =1 excited torsional state are based on measurements from previous studies performed in the 13–40GHz spectral range, as well as on new millimeter-wave measurements performed at Lille in the spectral range 75–465GHz. A few measurements and remeasurements in the 1.8–13GHz were also performed using the chirped FT-MW spectrometer located in North Texas. The pure rotational transitions in the far-infrared and in the microwave spectral range belonging to the two first torsional states have been globally fitted using the RAM (“Rho Axis Method”) dealing with the rotation–torsion Hamiltonian and implemented in the BELGI code. A total of 708 and 713 microwave transitions (6⩽ J ⩽40, ⩽23) belonging to the ground torsional state νt =0 and 1 have been fitted with root-mean-square (rms) deviations of 37.4kHz and 32.3kHz respectively, and 3170 pure rotational transitions in the far-infrared range (12⩽ Jmax ⩽65, 0⩽ ⩽48) belonging to νt =0 and 1 have been fitted with a rms deviation of 0.00017cm−1, using 35 parameters. Since in the far-infrared spectral range, the A–E internal rotor splittings have not been observed for the transitions belonging to the torsional ground νt =0 state of the cis-methyl nitrite species, another fit was performed on those lines, using a Watson type Hamiltonian for comparison. [Copyright &y& Elsevier]

Abstract: A search accelerated correct intensity Fourier transform microwave (SACI-FTMW) spectrometer has been used to rapidly record the rotational spectrum of pivaloyl chloride between 8 and 18GHz. Both a radio frequency and regular cavity-based instrument have then been used to obtain high resolution measurements below 4GHz and in the 4–18GHz regions, respectively. Rotational constants, centrifugal distortion constants, and chlorine nuclear quadrupole coupling constants have been determined for both the 35Cl and 37Cl isotopologues. The spectrum provides no evidence concerning internal rotation in the molecule. [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]