Zeeman effect resonance spectroscopy

Optical spectroscopy, Zeeman effect. Resonance scattering. 

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... 

Radford (1961, 1962) and Radford and Broida (1962) presented a complete theory of the Zeeman effect for diatomic molecules that included perturbation effects. This led to a series of detailed investigations of the CN B2E+ (v — 0) A2II (v = 10) perturbation in which many of the techniques of modern high-resolution molecular spectroscopy and analysis were first demonstrated anticrossing spectroscopy (Radford and Broida, 1962, 1963), microwave optical double resonance (Evenson, et at, 1964), excited-state hyperfine structure with perturbations (Radford, 1964), effect of perturbations on radiative lifetimes and on inter-electronic-state collisional energy transfer (Radford and Broida, 1963). A similarly complete treatment of the effect of a magnetic field on the CO a,3E+ A1 perturbation complex is reported by Sykora and Vidal (1998). The AS = 0 selection rule for the Zeeman Hamiltonian leads to important differences between the CN B2E+ A2II and CO a/3E+ A1 perturbation plus Zeeman examples, primarily in the absence in the latter case of interference effects between the Zeeman and intramolecular perturbation terms. 

Although the magnetic-field technique is commonly used in magnetic resonance and spectroscopy (like the Zeeman effect, magnetic optical rotation, and magnetic circular dichroism), its application to directly probing the dynamic processes of the excited electronic states of atoms and molecules... 

Laser-microwave spectroscopy based on nonlinear phenomena developed from the type of experiments on molecules already discussed in Section 3.2 which make use of optical pumping or double resonance. Occasionally, the laser and the rf power were high enough to create the nonlinear phenomena mentioned above, i.e., to saturate the transitions involved and/or to induce multiphoton transitions. The intermediate level in, e.g., two-photon transitions did not have to be a real state but could be virtual as well. Therefore, a drawback often encountered in earlier infared laser-microwave experiments could be avoided if the laser transition frequency did not exactly coincide with the molecular absorption line the Stark or Zeeman effect had to be used for tuning. This results in an undesired line splitting. With laser-microwave multiphoton processes, however, the laser can be operated at its inherent transition frequency. Exact resonance with molecular lines is then achieved by using a nonlinear effect, i.e., a radiofrequency quantum is added to or subtracted from the laser frequency (see Figure 28). 

Comparison with the Zeeman effect in optical spectroscopy. In optical double-resonance experiments the Doppler shift due to the motion of an atom through the r.f. magnetic field is negligible in comparison with the natural width of the excited levels. Substituting into equation (16.21) a typical atomic lifetime of 10" s leads to a line-width for the magnetic resonance signal, at low r.f. power of... 

Besides absorption and emission measurements, other techniques (optical, magnetic or magneto-optical) can also be used for determination and assignment of crystal-field energy levels inside the 4f shell two-photon absorption (TPA), Zeeman effect spectroscopy, electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD). 

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