Level crossing Zeeman

This method is equally applicable to atoms 26) and to molecules 22). In molecules the Zeeman splitting depends on the quantum number / of the total angular momentum and therefore the fluorescence from a single rotational level (v, f) need be observed. Because of this necessarily selective excitation, these molecular level-crossing experiments can be performed much more easily with lasers than with conventional light sources and have been sucessfully performed with Naj 2 > and NaK 29). 

Measurements of the Hanle effect and level crossings at magnetic fields B 0 showed for higher intensities of the excitation laser nonlinear Zeeman shifts [840]. 

Fig. 7.6 Hanle-effect and level crossings at S 0 in the S Ps/i-state of the Rb-isotope. The insert shows the nonlinear Zeeman-shifts...

There are, of course, also some disadvantages. One major problem is the change of the absorption profile with the magnetic field. The laser bandwidth must be sufficiently large in order to assure that all Zeeman components can absorb the radiation independent of the field strength B. On the other hand, the laser bandwidth should not be too large, to avoid simultaneous excitation of different, closely-spaced transitions. This problem arises particularly in molecular level-crossing spectroscopy, where several molecular lines often overlap within their Doppler widths. In such... 

B. Cahn et al., Zeeman-tuned rotational level crossing spectroscopy in a diatomic free radical. arXiv 1310.6450 [physics]... 

A.C. Luntz, R.G. Brewer, Zeeman-tuned level crossing in S CH4. J. Chem. Phys. 53,3380... 

Level-crossing spectroscopy is based on the measured change in the spatial intensity distribution or the polarization characteristics of fluorescence that is emitted from coherently excited levels when these levels cross under the influence of external magnetic or electric fields. Examples are fine or hyperfine levels with different Zeeman shifts, which may cross at a certain value Be of the magnetic field B (Fig. 12.1). A special case of level crossing is the... 

Because of the selection rule AM = 0, 1 we find that Kj 0 only for M-M = 0, 1 or 2. For M-M = 0 a level crossing cannot occur because of the non-crossing rule. Instead a related phenomenon, "anti-crossing" can be observed under certain circumstances [7.29]. For the arrangement shown in Fig.7.13 it can be shown that Kj = 0 for M-M = 1. If we now consider the special case where the sublevels of the excited state are linear Zeeman levels we have Ij m m I = 2/iggB/h for M-M = 2 yielding... 

We will conclude this section by illustrating how the tensor Stark polarizability constant can be measured using level-crossing spectroscopy. As illustrated in Fig.9,18, for the case of the potassium 5d 03/2 state the unknown Stark effect is measured in terms of the well-known Zeeman effect... 

Figure 5. Four-level hyperfine diagram illustrating manifold with sign of nuclear hyperfine coupling opposite that of nuclear Zeeman term, making it possible to adjust the Zeeman field so that the spin manifold levels cross.

Figure 12. Cross-relaxation between different types of nuclei ( H and Cl) in NMR as the nuclear Zeeman levels cross (adapted with permissi

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