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Dipole moment molecular beam measurements

Other measurements. Induced dipole moments can be measured by most of the familiar methods that are designed to measure permanent dipole moments. We mention in particular the beam deflection method by electric fields, using van der Waals molecules, and molecular beam electric resonance spectroscopy of van der Waals molecules [373, 193, 98]. [Pg.159]

Supermolecular spectra could perhaps be studied with state-selection using adequate molecular beam techniques. That would not be easy, however, because of the smallness of the dipole moments induced by in-termolecular interactions. For the purpose of this book, we will mostly deal with bulk spectra, or interaction-induced absorption of pure and mixed gases. A great variety of excellent measurements of such spectra exists for a broad range of temperatures, while state-selected supermolecular absorption beam data are virtually non-existent at this time. Furthermore, important applications in astrophysics, etc., are concerned precisely with the optical bulk properties of real gases and mixtures. [Pg.4]

Collision-induced dipoles manifest themselves mainly in collision-induced spectra, in the spectra and the properties of van der Waals molecules, and in certain virial dielectric properties. Dipole moments of a number of van der Waals complexes have been measured directly by molecular beam deflection and other techniques. Empirical models of induced dipole moments have been obtained from such measurements that are consistent with spectral moments, spectral line shapes, virial coefficients, etc. We will briefly review the methods and results obtained. [Pg.153]

The remaining error in the dipole moment Green8 attributes to lack of highly excited configurations. For open-shell molecules it is probable that Hartree-Fock results will be unreliable (see above) and a limited amount of Cl will be essential. Thus even for a Hartree-Fock function the calculated one-electron properties may not agree well with experiment (it should be remembered that, in the most favourable cases where the substance can be studied in a molecular-beam spectrometer and the dipole moment obtained from Stark effect measurements, the experimental error is much less than 0.001 D).28... [Pg.78]

Vibrational product state distributions have been obtained for reactions studied in crossed molecular beams using the technique of beam electric resonance spectroscopy [109]. This method uses the focusing action of electric quadrupole and dipole fields to measure the radio frequency Stark spectrum of the reaction products, which must possess a dipole moment. This has restricted this technique to reactions producing alkali halides. [Pg.373]

It is now possible to determine precise rotational spectra for hydrogen bonded molecules of moderate size and with even very small stabilization energies. Rotational constants, centrifugal distortion constants, electric dipole moments and nuclear hyperfine interactions have been measured for a considerable number of dimers using various microwave and molecular beam techniques. [Pg.110]

Ethylene has no dipole moment and a center of symmetry and therefore the Raman spectrum is an important source of structural information. After the early work on the rotational (Dowling and Stoicheff, 1959) and rovibrational Raman spectrum (Feldman et ah, 1956) these spectra were thoroughly studied in a series of publications (Hills and Jones, 1975 Hills et ah, 1977 Foster et ah, 1977). Overtones and combination bands were measured in an intracavity Raman experiment by Knippers et ah (1985). The Q-branch of the U2 band was resolved by pulsed CARS spectroscopy in a molecular beam experiment (Byer et ah, 1981). [Pg.294]

Among all the methods which have hitherto been brought forward for the determination of the electric dipole moment of molecules, the molecular-beam method occupies a special position, for it enables us to investigate the behaviour of individual free molecules in the electric field directly. It also has the great advantage that the effect of the field on the dipole moment of a single molecule occurs in it as a directly measurable quantity, so that it avoids the uncertainties of all other methods, which are chiefly due to the fact that in their case it is the macroscopic actions between the field and the dielectric (gas or liquid) which are measured and the mutual effects of the molecules can neither be eliminated entirely nor be allowed for accurately. [Pg.13]

The molecular-beam method has the further advantage that it can be used in many cases where the other methods cannot be applied. The methods in general use for the determination of dipole moments depend on the measurement of the dielectric constant of the substance in question in the form of vapour or of a dilute solution in a non-polar solvent, usually benzene. Many of the substances which do not dissolve to a sufficient extent in a solvent of this type and which cannot be transformed into vapour with a pressure suitable for the measurement of the dielectric constant can be investigated by means of the molecular-beam method, as the latter merely requires that it should be possible to sublimate the substance in a high vacuum. [Pg.13]

Molecular beam experiments on electric dipole moments are being prosecuted further in two directions. On the one hand, other substances in which the usual methods are inapplicable, but where a knowledge of the dipole moment is of interest from the viewpoint of structural chemistry, are being studied, and on the other hand, attempts are being made to work out a method which will enable us to measure the intensity distribution in the deflected beam and thus attain the real goal, namely the quantitative measurement of dipole moments by this method. [Pg.21]

The only disturbing effect of this kind which is involved in the measurement of dipole moments results from the fact, which, to be sure, is unavoidable, that in these experiments the molecules are always subjected to an external field. The fields commonly used in measuring dielectric constants are comparatively weak and would exceed about lOO volts per centimetre in exceptional cases only. Stronger fields are used in the molecular-beam method, but hitherto this method has always given the same qualitative results as the other methods in common use. It is also known that even the highest strengths of field obtainable have only a very slight effect on the numerical values of the dielectric constants of pure liquids. [Pg.46]

To sum up, the effect of an external field, i.e. the production of induced moments in molecules, whether the latter depend on Ppy P or Ppy can never give rise directly to a measurable contribution P<,. Theoretically an external field may indeed render anharmonic vibrations unsymmetrical and thus give rise to a measurable effect (see further below), but according to experiments by the molecular beam method this effect can only be made to account for a trifling part at most of the observed differences P — Pp or P — P oUd e dipole molecules Ca4 which were investigated. [Pg.52]

The value of the bond length is that measured by Akishin and Spiridonov (7) In a high-temperature electron diffraction study. Electron diffraction patterns (7) for SrBr were satisfactorily explained on the basis of a linear model (180 10 ). Later studies by Wharton et al. (8 ), using electric deflection of molecular beams to detect dipole moments, showed no polarity In the SrBtg molecule this Is most reasonably explained by a linear and centrosymmetrlc configuration. [Pg.493]

Dielectric and pressure virial coefficients of NzO have been measured at 6.5, 30.1, and 75.1 °C. The dipole moment, polarizability, and molecular quadrupole moment were determined to be 0.18 D, 3.03 x 1CT24 cm3, and 3.4 xlO 26 e.s.u. cm2, respectively.91 A lower limit of —0.15 0.1 eV has been calculated for the molecular electron affinity of N20, using molecular beam studies.92 The enthalpy-pressure behaviour for N20 along eleven isotherms in the vapour phase has been determined from measurements of the Joule-Thomson effect.91... [Pg.326]

The radiofrequency spectrum of phosphine has been measured in a molecular beam electric resonance spectrometer. The suspected inversion doubling was not observed its dipole moment (ju.) was 0.574 D. The calculated rotational barrier between the staggered and eclipsed conformers of methylphosphine is 1.83 and 1.71 kcal mol, in agreement with the experimental value of 1.96 from microwave measurements. An orbital-by-orbital analysis of the changes which occur upon rotation suggests a hydrogen-bond contribution when the phosphorus lone pair of electrons and a CH bond are appropriately orientated.The existence of a 1—2° tilt of a methyl group towards the phosphorus lone pair of electrons in methylphosphines (138) was a conclusion drawn from a microwave study... [Pg.278]

Experimental dipole moments can be obtained in several different ways. The first and most widely used approach is based on the measurement of dielectric constants. The second group of methods utilizes microwave spectroscopy and molecular beams (the Stark effect method, the molecular beam method, the electric resonance method, Raman spectroscopy, etc.). [Pg.235]


See other pages where Dipole moment molecular beam measurements is mentioned: [Pg.46]    [Pg.236]    [Pg.255]    [Pg.1297]    [Pg.394]    [Pg.470]    [Pg.264]    [Pg.418]    [Pg.706]    [Pg.374]    [Pg.505]    [Pg.147]    [Pg.299]    [Pg.312]    [Pg.6104]    [Pg.322]    [Pg.14]    [Pg.15]    [Pg.139]    [Pg.349]    [Pg.45]    [Pg.48]    [Pg.48]    [Pg.8]    [Pg.92]    [Pg.168]    [Pg.7]    [Pg.8]    [Pg.14]    [Pg.29]    [Pg.1297]   
See also in sourсe #XX -- [ Pg.48 ]




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