Rydberg States and the Zeeman Effect

The examples used here to illustrate the effects of a moderately strong magnetic field (Bz 1 Tesla) are from an experimental study of the NO nf — A2E+ transition probed by double resonance excitation via a selected rotational-Zeeman sublevel of the A2E+(w = 1) state. Individual nf(N+) 

An external magnetic field creates a spatial anisotropy in the laboratory frame, and the AN — 1, AMn = 0 off-diagonal matrix elements of the linear term in the Zeeman effect Hamiltonian (Eq. (6.5.38)) destroy N (but not Mn) as a good quantum number. The external magnetic field causes a transition from the usual Hund s case (d) hIIrN+N) scheme to the uncoupled case (d) 

8 cm-1 at n = 6 to 0.1 cm-1 at n = 30. The n-independent Zeeman splitting between mi, mi —l components, poBz = 0.5 cm-1, appears clearly at high-n. Each N+ level is split into (21 + 1)(2N+ + 1) Zeeman mi, M + (or, at low-n, lR, M ) components. Because N is destroyed by the magnetic field, most of the (21 + 1)(2N+ + 1) fine structure components of an N+ level in the nf — A2E+ transition have appreciable intensity. This is in marked contrast to the AN = Al propensity rule in a case (d) - case (b) transition. 

Perturbations affect the rate of absorption and emission of radiation in a fully understood and exactly calculable manner. They also affect the rates of chemical and collisional population/depopulation processes, but in a less easily estimated way. Perturbation effects on steady-state populations can be very large and level-specific. Although collision-induced transitions and chemical reactions are not governed by rigorous selection rules as are electric dipole transitions and perturbation interactions, some useful propensity rules have been suggested theoretically and confirmed experimentally. Gelbart and Freed (1973) suggested that the cross sections for collision-induced transitions between two different electronic states, E and E, are 

The Gelbart-Freed model is based on the assumption that this direct, electronically inelastic process is significantly less probable than the perturbation-facilitated one. This is a reasonable assumption in the case of electronic transitions involving a change of electron spin multiplicity (AS 0) or a small 

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