Magnetic field effects intramolecular states

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. 

Knowledge of the magnetic (and optical) properties of triplet states has been greatly enhanced by the development of zero-field (zf) resonance techniques, especially those employing optical detection. In what follows, we review the selection rules which govern the transitions in the zf experiment. We then present recent results from this laboratory on the lowest (nTc ) states of 1-halonaphthalenes and discuss in some detail the analysis of these spectra and their significance with respect to the intramolecular heavy-atom effect on the properties of the parent molecule. Next, we survey some representative results from other laboratories, including zf EPR, ODMR, ENDOR, and ELDOR experiments, and close with a brief description of other zf applications. 

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