T. R. Dyke

Radiofrequency and Microwave Spectrum of the Hydrogen Fluoride Dimer; a Nonrigid Molecule

The radiofrequency and microwave spectra of the K=0 states of (HF)2, (DF)2, and HFDF have been studied by the molecular beam electric resonance method. A unique hydrogen tunnelling motion involving the breaking and reforming of the hydrogen bond causes a splitting of rotational energy levels for (HF)2 and (DF)2, but not for HFDF. The electric dipole selection rules and nuclear spin statistics for the tunnelling molecules have been derived from a consideration of an extended permutation‐inversion group. Rotational constants, tunneling doublings, electric dipole moments, and deuterium quadrupole coupling constants have been determined from the observed spectra of the K=0 states. (HF)2(DF)2HFDF(B+C)/2 (MHz)6504.8±2.06252.194±0.0026500.1±0.1ν (MHz)19 776±121579.877 ±0.004μa  (D)2.987±0.0032.9919±0.00063.029±0.003(eqQ)Da (KHz)···110±8270±30 These results are interpreted with a semirigid, nonlinear model of the dimer geometry. The F—F distance is 2.79 ± 0.05 A, and the end hydrogen fluoride unit is bent from 60...

Electric Resonance Spectroscopy of Hypersonic Molecular Beams

A hypersonic nozzle beam (Mach 19) of HCN molecules was studied by electric resonance spectroscopy. Translational temperatures of 4°K and rotational temperatures of 64± 30°K were found from a 283°K nozzle source. The monoenergetic character of the beam and the rotational cooling lead to an order of magnitude increase in signal‐to‐noise ratios. The absence of an appreciable velocity dispersion and a homogeneous radiation field allowed a critical comparison with theoretical two‐level resonance lineshapes. An SF6 diluent was used to reduce the beam velocity by one‐half and increase spectral resolution over a thermal (effusive) source. SF6 vibrational relaxation was observed. Chemically interesting species can be formed: ArXe, XeHCl, (HCl)2, (HCN)x, and (HF)x.

Gas-phase structures and mass spectra of binary pentafluorides

Abstract Most known non-radioactive pentafluorides have been examined by molecular-beam mass spectrometry and by the deflection of molecular beams in inhomogeneous electric fields. Extensive association of the vapors occurs for all but the lighter pentafluorides and the interhalogens. The interhalogen pentafluorides are strongly polar, consistent with the accepted C4v symmetry. The transition-metal and Group V pentafluorides are all non-polar, except VF5 and CrF5 for which temperature-dependent polarity is observed. However, uncertainty exists as to whether these observations are applicable to monomeric pentafluorides in all cases. Mass-spectral cracking patterns are presented for all species.

Electric Deflection of Molecular Beams of Carbon Suboxide and Carbon Subsulfide

The deflection behavior of molecular beams of C3O2 at 200 and 300°K and C3S2 at 300°K has been studied in inhomogeneous electric fields. Both species show net defocusing of the scattered beam with applied field. By comparison with the bent molecule NO2 whose electric dipole moment is known, upper limits of 0.15 D were placed on the electric moments of C3O2 and C3S2. These limits, coupled with extimates of the integrated absorption intensities obtained from published spectra for the ν7 vibration, permit upper limits of 0.15 rad to be placed on the bending angle. The most probable configuration is thus linear.

Molecular beam electric deflection of the tetrahalides CF4, CCl4, SiF4, SiCl4, GeCl4, TiF4, TiCl4, VF4, and VCl4

Using molecular beam electric deflection, the temperature dependence of polar behavior has been studied for the molecules CF4, CCl4, SiF4, SiCl4, GeCl4, TiF4 TiCl4, VF4, VF4, and VCl4. A number of these molecules show polar behavior consistent with a vibrationally induced dipole moment for states with one or both of the triply degenerate vibrations excited. In four of the tetrachloride species, the presence of a vibrationally induced dipole moment was confirmed by the change in polar behavior with isotopic substituion of the Cl atoms. The deflection behavior of the transition metal tetrahalides varied from nonpolar in VCl4 to very polar in TiF4.

Stark energies for molecules with vibrationally induced dipole moments

For the various classes of molecules capable of having vibrationally induced electric dipole moments, explicit expressions for the resultant Stark energies are derived. In addition, the change in the vibrationally induced Stark effect with isotopic substitution of the B atoms in a tetrahedral AB4 molecule is considered.