Zeeman effect measurements

Finally, there are numerical relationships between groups of transitions which share common levels these relationships correspond to combination differences in other branches of spectroscopy. Through a combination of these relationships, double resonance studies and Zeeman effect measurements, it was possible to establish the energy level diagram shown in figure 10.74. Each level is characterised by its parity and J value the observed transitions are also shown in figure 10.74. The important task... 

We have, we hope, provided enough detail about the Zeeman effect to show how almost every microwave resonance could be assigned, so far as the J values were concerned. A final remark should be made concerning the parity labels. These depend upon the identification of a J = 1 /2 <- 1/2 transition, and the measured g-factors for the two J = 1/2 levels which identify their e//, and hence total parities. The parities of all other levels then follow because all transitions are electric-dipole allowed, between states of opposite parity. As we have mentioned earlier, the combination of numerical relationships between the resonance frequencies, double resonance studies, and Zeeman effect measurements enabled the pattern of levels lying within 8 cm 1 of the dissociation limit to be established. The highest level, J = 7/2 (—parity), in figure 10.74, was thought to lie within 20 MHz (<0.001 cm-1) of the dissociation limit. 

In theoretical interpretations of their electronic [Gouterman (85), Simpson (160), Weiss (199)] and pmr spectra [Jackman (105)] porphyrins have often been treated as cyclic polyene hydrocarbons, and it has recently been demonstrated that the (16)-annulene n dianion (which has 18 n electrons, is planar and aromatic) does indeed perfectly reproduce the spectra of porphyrin species with D,m symmetry [Oth (137)]. The analogy between aromatic hydrocarbons and the porphyrins stands on solid experimental and theoretical ground, and redox potentials together with any coupling constants from esr experiments should yield equally straightforward correlations. Zeeman effect measurements also support this conclusion [Malley (126)]. 

Fig. III.2. Electromagnet used for the rotational Zeeman effect measurements at Kiel. The upper yoke may be lifted by hydraulic jacks in order to insert spacers on top of the side yokes for different gap widths. Bearings in the side yokes are to allow for lateral access of the gauss-meter probe tip. The power connections (/mu = Amps, each coil) arc visible at the right front side. The overall length of the gap is 250 cm and the maximum field at a gap width of 6 cm is close to 21 kG, and at a gap of 0.6 cm the field is 31 kG...

Using a high-temperature microwave spectrometer capable of making Zeeman-effect measurements in strong magnetic fields (up to 50 kG), the gj factor [0.05370 (15)] and the magnetic susceptibility anisotropy [600(200) Hz kG ] of TIF have been determined. ... 

From accurate measurements of the Stark effect when electrostatic fields are applied, information regarding the electron distribution is obtained. Further Information on this point is obtained from nuclear quadrupole coupling effects and Zeeman effects (74PMH(6)53). 

In the previous section it has been shown that the measured sample absorbance may be higher than the true absorbance signal of the analyte to be determined. This elevated absorbance value can occur by molecular absorption or by light scattering. There are three techniques that can be used for background correction the deuterium arc the Zeeman effect and the Smith-Hieftje system. 

In practice, the emission line is split into three peaks by the magnetic field. The polariser is then used to isolate the central line which measures the absorption Ax, which also includes absorption of radiation by the analyte. The polariser is then rotated and the absorption of the background Aa is measured. The analyte absorption is given by An — Aa. A detailed discussion of the application of the Zeeman effect in atomic absorption is given in Ref. 51. 

In the method described by Willie et al. [167] atomic absorption measurements were made with a Perkin-Elmer 5000 spectrometer fitted with a Model HGA 500 graphite furnace and Zeeman effect background correction system. Peak absorbance signals were recorded with a Perkin-Elmer PRS-10 printer-sequencer. A selenium electrodeless lamp (Perkin-Elmer Corp.) operated at 6W was used as the source. Absorption was measured at the 196.0nm line. The spectral band-pass was 0.7nm. Standard Perkin-Elmer pyrolytic graphite-coated tubes were used in all studies. 

The observation of natural ORD or CD requires lack of symmetry in the molecule, but any molecule may exhibit magnetic circular dichroism (MCD). It constitutes a molecular analogy for the Zeeman effect in atomic spectra. Measurements in this area may well reveal substituent interactions which are masked in normal UV spectra. Extensive definitive papers of great interest which well illustrate this have appeared on MCD of pyridine derivatives, measured in cyclohexane, acetonitrile, and alcohol or aqueous acidic solutions for protonated... 

The stabilized temperature platform furnace (STPF) concept was first devised by Slavin et al. It is a collection of recommendations to be followed to enable determinations to be as free from interferences as possible. These recommendations include (i) isothermal operation (ii) the use of a matrix modifier (iii) an integrated absorbance signal rather than peak height measurements (iv) a rapid heating rate during atomization (v) fast electronic circuits to follow the transient signal and (vi) the use of a powerful background correction system such as the Zeeman effect. Most or all of these recommendations are incorporated into virtually all analytical protocols nowadays and this, in conjunction with the transversely heated tubes, has decreased the interference effects observed considerably. 

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