Anticrossing spectroscopy

In practice there are several factors which complicate anticrossing spectroscopy. The four anticrossings of Fig 18.4 apparently occur at the same field, given... 

Beyer, H.J. and Kleinpoppen, H. (1979). Applications of anticrossing spectroscopy, Proc. VI Intern. Conf. Atomic Phys., Zinatne, Plenum Press, Riga, New York, London, pp. 435-461. 

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. 

Miller, et al., (1974) used MOMRIE (Microwave Optical Magnetic Resonance Induced by Electrons) complementarily with anticrossing spectroscopy in experiments on He, H2, and other molecules. Small differences in electron bombardment excitation cross-sections combined with different radiative lifetimes lead to steady-state population differences between initial and final levels of the microwave transition. By monitoring fluorescence from one of the two involved electronic states, a change in fluorescence intensity signals a microwave resonance. Electron bombardment excitation tends to produce smaller population differences than the chemical pumping scheme exploited in the CN experiments, but the MOMRIE technique is more generally applicable. 

The level-crossing and anticrossing phenomena have been observed for the first time for hyperfine components of atomic energy levels.The level-anticrossing spectroscopy was then applied to the study of very weak singlet-triplet (or doublet-quadruplet) coupling in atoms" and in diatomic molecules (see, e.g.. Refs. 124 and 125 and references therein). 

H.J. Beyer, H. Kleinpoppen, Anticrossing spectroscopy, in Progr. Atomic Spectroscopy, ed. by W. Hanle, H. Kleinpoppen (Plenum, New York, 1978), p. 607... 

A perturbation acts as a window through which normally unobservable states may be viewed. Anticrossing, quantum-beat, and MODR spectroscopies are capable of examining the states in the immediate vicinity of the perturbed level. Optical-optical double resonance (OODR) allows systematic exploration of states far above and below the perturbed level. Gottscho, (1979) utilized an... 

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