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The rotational spectra of six isotopologues of pyridine-xenon, two isotopes of the nitrogen atom (14N and 15N) in pyridine with three isotopes of the rare gas atom (129Xe, 131Xe, and 132Xe) have been measured by pulsed jet Fourier transform microwave spectroscopy. The complex has a structure with the xenon atom located in the plane of symmetry perpendicular to the aromatic ring plane. Its distance from the center of mass of pyridine is 3.81 Å, and it is tilted—with respect to the c principal axis of pyridine—by 7° toward the N atom. The 14N and 131Xe nuclear quadrupole coupling constants have been determined for the isotopologues containing these nuclei. Information on the dynamics of the Xe van der Waals motions was obtained from the centrifugal distortion and from the changes in the planar moments of inertia in going from pyridine to pyridine...Xe. [ABSTRACT FROM AUTHOR]

The rotational spectra of 2 isotopologues of the molecular adduct CH2F2–CH2ClF show that the two subunits are held together through two weak C–H…F–C and one C–H…Cl–C linkages, rather than through three weak C–H…F–C connections. This suggests the weak Cl…H interaction to be observed preferentially to a weak F…H one. Structural information on these weak hydrogen bonds has been obtained. The dissociation energy has been estimated from centrifugal distortion to be 5.3 kJ mol−1. [ABSTRACT FROM AUTHOR]

Abstract: Differently from acetylacetone, hexafluoroacetylacetone is a ‘rigid’ molecule on the scale time of microwave spectroscopy. Its rotational spectrum, corresponding to the enolic C s form, does not display any doubling of rotational lines, indicating high effective barriers to the internal motions. An accurate structure of the main frame of the molecule has been obtained from the rotational spectra of nine isotopic species, measured by pulsed jet Fourier-transform microwave spectroscopy. The keto form lies, according to MP2/6-311++G(d,p) ab initio calculations, about 14kJ/mol higher in energy. [Copyright &y& Elsevier]