Condensed phase structures reflectivity measurements

Experimentally, free-ion spectra (both neutral and ionic species) are usually observed in emission, and the energy level structure is deduced from coincidences of energy differences of pairs of spectral lines, subject to verification by isotope shift, hyperfine structure and magnetic gf-factor tests. In condensed phases, spectra are more commonly measured in absorption. Relative intensities associated with parity-allowed and forbidden transitions are reflected in the nature of two processes transitions in which the initial and final states belong to electronic configurations of different parity (parity-allowed transitions, e.g. 5f - 5f 6d) and those in which both states belong to the same configuration (parity-forbidden transitions, e.g. 5f 5f ). The latter are weak and sharp. The... 

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