Conformation and stability of the hydrogen-bonded complex 6-oxabicyclo

The hydrogen-bonded complex between 6-oxabicyclo[3.1.0]hexane and hydrogen chloride was investigated by microwave spectroscopy in a supersonic jet. A dual flow pulsed valve was used to preclude chemical reaction between the monomers. Only the equatorial conformer was observed and the spectra of three isotopomers, (C5H8O, H35Cl), (C5H8O, H37Cl) and (C5H8O, D35Cl), were measured. The derived structure of the complex has Cs symmetry with the hydrogen chloride pointing to the domain of the equatorial lone pair of electrons at the oxygen atom. The three atoms involved in the hydrogen bond adopt a bent arrangement with a O...H distance of 1.77(4) A, a (O...H-Cl) angle of 115(4)degrees, and a deviation of 15.4(14)degrees of the hydrogen bond from collinearity. In agreement with the experimental results, ab initio calculations predict the equatorial form to be the most stable one.

The Ground and First Torsional States of CD(3)CHO.

The rotational spectra for the ground and first excited torsional states v(t) = 0 and 1 in the frequency region of 8-254 GHz and the v(t) = 1 <-- 0 band high-resolution far-infrared spectrum of 2,2,2-d(3)-acetaldehyde (CD(3)CHO) were measured. We fitted a data set consisting of 1016 v(t) = 1 <-- 0 far-infrared lines together with 195 microwave lines in v(t) = 0 and 79 microwave lines in v(t) = 1 to near-experimental accuracy, using a global model from the earlier literature. The final fit includes lines with J

Investigation of the Rotational Spectrum of Pyrimidine from 3 to 337 GHz: Molecular Structure, Nuclear Quadrupole Coupling, and Vibrational Satellites.

A comprehensive reinvestigation of the rotational spectrum of pyrimidine was carried out by using several different spectrometers. All singly substituted 13C- and 15N-isotopic species of pyrimidine have been measured in natural abundance with millimeter-wave free jet and waveguide Fourier transform microwave techniques, and complete rs and r0 heavy atom geometries have been determined. The ground state rotational spectrum in the centimeter-wave region was measured at sub-Doppler resolution of the cavity Fourier transform spectrometer and all elements in the inertial and principal nuclear quadrupole-coupling tensors of the nitrogen nuclei in pyrimidine have been determined. The room-temperature spectrum was measured up to 337 GHz and J = 66 with BWO-based spectrometers and sextic level centrifugal distortion constants in the rotational Hamiltonian have been determined for the ground state and three lowest vibrational fundamentals of pyrimidine. Copyright 1999 Academic Press.

Rotational Spectrum of Vinylarsine.

The rotational spectrum of vinylarsine in the ground state has been studied in the range 7-320 GHz. The spectra of a syn conformer and a gauche conformer have been unambiguously assigned on the basis of the existence of a b-type or a c-type spectrum. Rotational constants, quartic, and some sextic centrifugal distortion constants were derived. For the syn form, measurements of low J aR0,1 transitions in a pulsed-nozzle Fourier transform microwave spectrometer (FTMWS) enabled the determination of the diagonal elements of the quadrupole tensor, as well as two spin-rotation constants. Ab initio calculations performed at the MP2 level using the 6-311++G(3df, 3pd) basis set reproduced experimental rotational constants within 0.2%. Copyright 1998 Academic Press.

Characterization of nanophase Al-oxide/Al powders by electron energy-loss spectroscopy.

Al nanoparticles were prepared by the inert gas condensation method. After passivation with oxygen and air exposure we obtained a powdered sample of an Al-oxide/Al nanocomposite material. In the present paper we describe the use of the electron energy-loss spectroscopy (EELS) technique in a transmission electron microscope to characterize such nanostructured powders compared with a microcrystalline commercial aluminium foil. Energy-filtered images showed the presence of an alumina overlayer of approximately 4 nm covering the aluminium nanoparticles (23 nm in diameter). EELS analysis enabled us to determine the total amount of Al2O3 and metallic Al and the structure of the alumina passivation overlayer in the sample. In particular, the extended energy-loss fine structure analysis of the data showed a major presence of Al tetrahedrally coordinated with oxygen in the alumina passivation layer of Al nanoparticles instead of the octahedral coordination found for a conventional Al foil. This surprising effect has been attributed to the nanoscopic character of the grains. The analysis of the electron-loss near-edge structure also determines the presence of a certain degree of aggregation in this kind of powdered sample as result of the coalescence of the nanocrystalline grains. The procedure presented here may have the potential to solve other problems during characterization of nanostructured materials.

The Millimeter-Wave Spectrum of 2,3-Dihydrofuran

The millimeter-wave spectrum of 2,3-dihydrofuran in the ground and five ring-puckering excited states has been measured in the frequency range 100-250 GHz. The ground and first ring-puckering excited states have been fitted to a two-state Hamiltonian including Coriolis coupling interaction. The determined energy difference of 18.684(7) cm-1 between these states and the a and b type coupling parameters are consistent with the ring-puckering potential function and the previously observed dependence of the centrifugal distortion constants DeltaJK, DeltaK, and deltaK. A small ring-puckering dependence of the quartic centrifugal distortion constants DeltaJ and deltaJ has been also observed. This dependence is well accounted for in terms of the ring-puckering potential function and the vibrational dependence of the rotational constants.