Ewa Białkowska-Jaworska

The structure of cyclohexane, F-, Cl-, Br- and I-cyclohexane

Abstract The ground state, r0, and the average, r∗ , structures of cyclohexane were determined from the recently reported rotational constants for several isotopic species of cyclohexane. These structures provide a better description of the heavy atom skeleton in cyclohexane than the rs structure and allow an accurate prediction of the rotational constants for C6H12 and C6D12. The new structure for cyclohexane was combined with ab initio calculations to redetermine the key structural features of F-, Cl-, Br- and I-cyclohexane, and it is found that while the equatorial CX bond lengths are comparable with those for secondary substitution in propane, the axial bond lengths are all longer and halfway between those for secondary and tertiary substitution.

The structure and electric dipole moment of camphor determined by rotational spectroscopy

The rotational spectrum of camphor was investigated for the first time. Accurate spectroscopic constants for the parent isotopomer were determined from measurements in supersonic expansion at 6.7–18.5 GHz, and on a room-temperature sample at 173–222 GHz. All three types of allowed dipole moment transitions, μa, μb, μc, were observed. The supersonic expansion spectrum allowed measurement, in natural abundance, of all ten singly substituted 13C isotopomers, as well as of the 18O isotopomer. The rotational constants were used to determine the rs, r0, and the r(1)m gas-phase geometries of the camphor molecule. The electric dipole moment of camphor was determined from Stark effect measurements, and is |μa| = 2.9934(23) D, |μb| = 0.7298(6) D, |μc| = 0.0804(7) D, μtot = 3.0821(22) D. The experimental results are compared with predictions from ab initio calculations and with the geometry of solid camphor.

The Millimeter- and Submillimeter-Wave Spectrum of the trans-trans Conformer of Diethyl Ether (C2H5OC2H5)

Since dimethyl ether is found to have a high abundance in hot cores, it is reasonable to search among such sources for detectable abundances of the more complex analogs ethyl methyl ether (C2H5OCH3) and diethyl ether (C2H5OC2H5). Indeed, preliminary detections of both complex ethers have been reported. Definitive interstellar searches do require laboratory spectra, however, but for many years only low-frequency data have been available for both of these species. Following our recent study of the millimeter-wave and submillimeter-wave spectrum of ethyl methyl ether, we report here the study of the millimeter- and submillimeter-wave spectrum of the lowest energy conformer of diethyl ether. With four different spectrometers, over 1000 new spectral lines have been measured and analyzed at frequencies up to 350 GHz. Fitting the data to a set of spectroscopic parameters from the Watson A-reduced form of the asymmetric-top Hamiltonian has allowed us to predict the frequencies and intensities of many more transitions through 400 GHz. A more precise determination of the electric dipole moment of diethyl ether was also carried out, resulting in μ = μb = 1.0976(9) D.

Rotational spectroscopy of cf2clccl3 and analysis of hyperfine structure from four quadrupolar nuclei

CF2ClCCl3 has recently been identified among several new ozonedepleting substances in the atmosphere.a There are no literature reports concerning rotational spectroscopy of this molecule, although we were recently able to report its first chirped pulse, supersonic expansion spectrum.b CF2ClCCl3 has a rather small dipole moment so that the spectrum is weak and each transition displays very complex nuclear quadrupole hyperfine structure resulting from the presence of four chlorine nuclei.

ROTATIONAL SPECTROSCOPY OF NEWLY DETECTED ATMOSPHERIC OZONE DEPLETERS: CF3CH2Cl, CF3CCl3, AND CF2ClCCl3

Three of the four compounds have non-zero dipole moments and are amenable to study by rotational spectroscopy, establishing the basis for analytic applications. Relatively limited studies have been reported for CF3CH2Cl and CF3CCl3, while CF2ClCCl3 has not yet been studied by this technique. We presently report extensive results obtained for all three compounds, resulting from concerted application of supersonic expansion FTMW spectroscopy in chirped pulse and cavity modes, and room-temperature MMW spectroscopy. Among the plentiful results, we have been able to resolve and fit the complex nuclear quadrupole hyperfine splitting.