Radiation-induced energy shift

Figure 1.1 One of 48 time-orderings contributing to radiation-induced energy shift with scattering taking place at different centers.

Another major advantage associated with the induced moment method is that it is easy to generalize the results for fhe radiation-induced energy shift to more than two interacting particles. From the form of the expression for the two-body potential (46), the extension to n bodies is compactly written as follows [54] ... 

For a free electron, the Dirac theory yields a value gfree = 2. Corrections to the free-electron g-factor are essentially due to the interaction with the free radiation field. The determination of the g-factor of a bound electron interacting with an additional, homogeneous magnetic field Bext via measurements of the induced energy shift on atomic levels is one of the basic experiments for testing QED. The deviation (g — 2) can be measured rather precisely. 

A second example, mentioned already, is microwave spectroscopy of Rydberg levels that have been excited by resonant two-step absorption of two dye lasers (Fig. 5.41b). The high accuracy of microwave spectroscopy allows the precise determination of finer details, such as field-induced energy shifts of Rydberg levels, broadening of Rydberg transitions by blackbody radiation, or other effects that might not be resolvable with optical spectroscopy. 

The total laser-induced intermolecular energy shift is given by the sum of the two contributions (31) and (34) and applies for radiation propagating in a fixed direction relative to the two oriented molecules. A molecular average can be carried out for all possible orientations of A and B relative to each other. In this case, the static contribution (34) vanishes while the dynamic term becomes... 

A. Salam, Two Alternative Derivations of the Static Contribution to the Radiation-Induced Intermolecular Energy Shift. Phys. Rev. A 76 (2007) 063402. 

Several important effects are equilibrium in nature, for example spectral shifts associated with solvent induced changes in solute energy levels are equilibrium properties of the solvent-solute system. Obviously, such observables may themselves be associated with dynamical phenomena, in the example of solvent shifts it is the dynamics of solvation that affects their dynamical evolution (see Chapter 15). Another class of equilibrium effects on radiation-matter interaction includes properties derived from symmetry rules. A solvent can affect a change in the equilibrium configuration of a chromophore solute and consequently the associated selection rules for a given optical transition. Some optical phenomena are sensitive to the symmetry of the environment, for example, surface versus bulk geometry. 

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