T. A. Dixon

Molecular beam studies of benzene dimer, hexafluorobenzene dimer, and benzene–hexafluorobenzene

A detailed study of the electric deflection of molecular beams of (C6H6)2, (C6F6)2, and C6H6–C6F6 is reported. Although no resolved microwave or radio frequency transitions were observable, examination of unresolved beam transitions at radio frequencies were useful in establishing that the homomolecular dimers (C6H6)2 and (C6F6)2 are asymmetric rotors while the heteromolecular dimer C6H6–C6F6 is a symmetric top. From analysis of the quantitative electric deflection the dipole moment of C6H6–C6F6 is 0.44±0.04 D.

Determination of the structure of ArCO2 by radio frequency and microwave spectroscopy

The species ArCO2 produced by adiabatic expansion is structurally characterized by molecular beam electric resonance spectroscopy. ArCO2 is shown to have C2v symmetry. The spectroscopic constants obtained are: The derived structural constants for ArCO2 are: Comparison is made with a number of proposed Ar–CO2 intermolecular potentials. The determined force constants are shown to be poorly fitted by a spherical argon–oxygen interaction.

CO2–HF: A linear molecule

The results of microwave and radio frequency spectroscopy of the weakly bound complexes of hydrogen fluoride with carbon dioxide and carbonyl sulfide are presented. The following spectroscopic constants are determined: A nearly linear hydrogen bonded equilibrium structure with an O–H bond length of ∼1.9 A is consistent with all the experimental data. The stretching force constant, estimated from the distortion constant to be ks = 0.021 mdyne/A for CO2–HF, appears anomalously small for such a short bond.

The rotational and hyperfine spectrum of Ar–HF

The radio frequency and microwave spectrum of Ar–HF has been remeasured by molecular beam electric resonance spectroscopy. Analysis of the data yields a revised value for the HF nulear spin–spin constant S, which in turn provides information about the vibrationally averaged geometry of the complex. Rotational and hyperfine constants and the dipole moment have also been measured for Ar–DF: The average structures and estimated harmonic force constants are shown to be consistent with those observed for other Ar–HX complexes. Comparison of the two hyperfine constants for Ar–DF indicates that the average charge distribution around the deuterium is only weakly perturbed by the argon atom.

The structure of N2O–HF

The rotational spectra of four isotopes of the weakly bound complex N2O–HF have been measured by molecular beam electric resonance spectroscopy. The following spectroscopic constants and structural parameters were derived from the observations: In the average structure, the N2O axis makes an angle of ∼47° with a line rc.m. drawn between the centers of mass of the two submolecules. HF is hydrogen bonded toward the oxygen on N2O to form an angle of ∼31° with the center of mass line.

The structure of Ar–N2O

The rotational spectra of two isotopes of the weakly bound complex Ar–N2O have been measured by molecular beam electric resonance spectroscopy. The following spectroscopic constants and structural parameters were derived from the observations: In the average semirigid structure, the Ar is 3.460(5) A distant from the center of mass of N2O and 7.4°(2) to either side of a line perpendicular to the N2O axis at the center of mass. Analysis of the moments of inertia of the two isotopic species and the measured dipole moments, with a classical harmonic bender model, indicates that the equilibrium Ar–N–O angle is 87±1.5° and that the sign of the N2O dipole moment is +NNO−.

Microwave and radio frequency spectra of Xe–HF

The spectroscopic constants for Xe–HF obtained from molecular beam electric resonance spectroscopy are as follows: The structure and weak bond force constants derived from the spectroscopic constants are consistent with data on other noble gas–hydrogen fluoride complexes. It is found that the electric field gradient at the Xe nucleus for a given HF orientation scales with the electric field gradient arising from HF.

The structure and hyperfine constants of HF–Cl2

Molecular beam electric resonance studies on two isotopes of HF–Cl2 have enabled the following spectroscopic constants to be determined: These constants are best interpreted in terms of an equilibrium structure for HF–Cl2 in which the three heavy atoms form a linear array with an F–Cl bond length of 2.96 A. The proton is off‐axis with an H–F–Cl angle of 125°. The chlorine quadrupole coupling constants show a charge distortion of the chlorine submolecule. Precise interpretation of eQq is hindered by lack of a value for the coupling constant of free 35Cl2.

The microwave spectrum of argon methyl chloride

Molecular beam electric resonance spectroscopy of the complex ArCH3Cl is reported. The spectra, only observable at low resolution (3 MHz), are complex and not analyzed. No evidence was found for a symmetric rotor spectrum comprising part of the observed features. It is concluded that the molecular structure of the complex consists of Ar binding off the C–Cl axis.