Dipole moment Stark effect

Measurements of Stark splittings in microwave and radiofrequency spectra allow tliese components to be detennined. The main contribution to tire dipole moment of tire complex arises from tire pennanent dipole moment vectors of tire monomers, which project along tire axes of tire complex according to simple trigonometry (cosines). Thus, measurements of tire dipole moment convey infonnation about tire orientation of tire monomers in tire complex. It is of course necessary to take account of effects due to induced dipole moments and to consider whetlier tire effects of vibrational averaging are important. 

The orientation of the dipole moment, experimentally established by the Stark effect (158), can also be compared to the calculated ones (Fig. 1-5). 

Using the Stark effect, the dipole moment of, for example, CH3F has been found to be... 

Dipole moments of asymmetric rotors or, strictly, their components along the various inertial axes, may be determined using the Stark effect. 

Atomic charges (q ) Dipole moments [57] QM, dielectric permittivity, Stark effect, microwave... 

These can be determined experimentally to very high accuracy from the Stark effect and molecular beam studies. The experimental accuracy is far beyond the capabilities of ab initio studies. At the other extreme, the original route to these quantities was through studies of the dielectric polarization of species in solution, and there is currently interest in collision-induced dipole moments. In either case, the quantities deduced depend critically on the model used to interpret the experiment. 

Standar model (SM), particle physics, electron electric dipole moment, 242-243 Stark effect, permanent electric dipole moment, 245-249... 

From a study of the microwave spectrum of 2-methylselenophene, the second-order Stark effect in the ground state was determined.11 The technique used was double radiofrequency-microwave resonance. For the identification by the double resonance method transitions of chiefly the A-state were chosen. From these observations the components of the dipole moment of 2-methylselenophene and the total dipole moment were determined. 

Breslow etal.133 investigated the microwave spectrum of cyclopropenone and determined data for bond lengths, bond angles, dipole moment (4.39 D from the molecular Stark effect), and magnetic susceptibility anisotropy (Ax) as seen in Table 5 in comparison with cyclopropene5 3 ... 

Tables 1, 2, and 3 present a set of five alcohols. In Table 1, it should be noted that while MM3(96) calculates the magnitude of the dipole moment to be essentially the same for the entire set of molecules, MM3(2000) is superior in reproducing the experimental dipole moments. This is demonstrated by comparing the root mean squared deviation of 0.0878 Debye in MM3 to the 0.0524 Debye deviation in MM3(2000). (All of the experimental values except where notes are stark effect measurements determined from microwave spectra.)...

The rotational spectrum of 1,2-dithiin was measured using a pulsed-beam microwave spectrometer in the 8-18 GHz range <1996JSP(180)139> by Stark effect measurements, the electric dipole moment was also determined (/ta = 1.85 D). The molecule proved to be of C2 symmetry with a twisted conformation about the S-S bond and a C-S-S-C dihedral angle of 53.9... 

From microwave spectra, in the presence of a uniform electric field applied to the gas (Stark effect), it is possible to obtain accurate measurements of dipole moments. 

Values of /rc and /iceq were obtained from the linear Stark effects, and, making the assumption that the total dipole moment of both conformers is the same, then nf /paeq was estimated. Substitution in the equation gave AE = 245 + 150 cal mol 1 corresponding to 60% N-Heq conformer at 20°C.144 The validity of the assumption of equal overall dipole moments of the two conformers has been challenged.9... 

Aliphatic ketones show broad, low-intensity absorption maxima in the vicinity of 280 nm which are a result of n - n transitions. By use of the Stark effect, Freeman and Klemperer estimated that the dipole moment in the n, n singlet state is reduced to 1.48 D from its ground state value of 2.34 D [253]. 

The experimental values for the dipole moment of furan vary somewhat according to the method used and to the conditions employed it is now agreed, however, that the use of the Stark effect in microwave spectroscopy gives the most accurate result (0.661 D) for the gas phase (51JCP(19)1609). In the past, values up to 0.72 have been used, especially for... 

The dipole moments of pyran-4-one and the corresponding thione have been determined from Stark effects <81JCS(F2)79) and the values compare favourably with those obtained from dielectric measurements <52AC(R)673). Their magnitudes (ca. 4 D) are higher than calculated, suggesting some contribution from polar canonical forms to the actual structure of the molecule. The implication to the aromaticity of pyranones is discussed in more detail in Section 2.22.8.1. 

Sheridan and co-workers144 took the microwave spectra of oxadiazole after its synthesis in 1962.39 From an analysis of Stark effects for a number of transitions, they concluded that the dipole moment should be 1.2 0.3 D (Table II). Davies and Mackrodt139 calculated the dipole moment to be 1.34 D, within the experimental error of Sheridan s value, by the CNDO/2 method of Pople and Segal. Other calculations133,136,138 indicate that the dipole moment of 1,2,4-oxadiazole should be notably less than that of the 1,2,5- and 1,3,4-isomers. Direct measurements of dipole moments by Milone145 had portended this much earlier. Besides the ones given in Table II, Milone had also found the same range of dipole moments for 3-methyl-5-phenyl, 5-methyl-3-phenyl, and other derivatives of the three sets of isomeric oxadiazoles. 

Fig. 6.1 Charge distribution for H, for parabolic eigenstates n = 8, m = 0, nt — / = —7 to 7. The dipole moments that give rise to the first order Stark effect are conspicuous (from...

When a) l/n3, the field required for ionization is E = 1/9n4, and as a> approaches l/n3 it falls to E=0.04n. These observations can be explained qualitatively in the following way. At low n, so that a> 1/n3, the microwave field induces transitions between the Stark states of the same n and m by means of the second order Stark effect. With only a first order Stark shift a state always has the same dipole moment and wavefunction, as indicated by the constant slope dW/d of the energy level curve. Thus when the field reverses, — — , the Rydberg electron s orbit does not change. With a second order Stark shift as well, the slope dW/d is not the same at E and —E, and as a result the dipole moment and wavefunction are not the same. If the field is reversed suddenly a single Stark state in the field E is projected onto several Stark states of the same n and m when E — - E. Since all the Stark states of the same n make transitions among themselves they ionize once the field is adequate to ionize one of them, the red one, at E = 1/9n4 for m n. 

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... 

Pochan, Baldwin and Flygare have analyzed the microwave spectra of cyclopropanone and the isotopic isomers 13Ci, 13C2, and 2,2-dideutero-cyclopropanone.63) The rotational transitions were determined by studying the Stark effect (the shifts and splittings of lines produced by an electric field). The type of transition observed for cyclopropanone was consistent with C v symmetry and the sum of the moments of inertia (/a + /b — Ic) suggested that all four protons are out-of-plane. These data eliminate such structural alternatives as the dipolar oxyallyl tautomer 82 and allene oxide 83. The electric dipole moment (fi ) was calculated to be 2.67 0.10 D, which corresponds to an average of those of acetone (2.93 D) 65> and formaldehyde (2.34D).6 )... 

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