Band intensity anomalies

Perturbations between States of the Same Symmetry Vibrational-Band Intensity Anomalies.380... 

If the experimental lineshapes do not exhibit sub-bands and are asymmetric, or if they involve sub-bands, but with intensity anomalies with respect to the Franck-Condon progression law, then, together with the dephasing mechanism, damping of the slow mode ought to be also considered as occurring in a sensitive competitive way. 

Band intensities some spectral bands involving electronic transitions have intensities other than those which might be expected in terms of a purely ionic model. This evidence tends to be more speculative than the others listed above and so it has not been discussed earlier in the text. There are four intensity anomalies which may be taken to indicate covalency. 

Routine measurements of d-d spectra are performed on solutions. If a suitable solvent cannot be found for a solid sample, a diffuse reflectance spectrum of a powdered sample can be taken. This is actually an absorption spectrum of the surface layers of the sample and is subject to a number of anomalies and artefacts. It is much better to study microscopic single crystals, preferably at low temperatures. Large crystals (if they can be grown) tend to absorb too strongly around band maxima small, thin (c. 0.01mm) plates are best. It is usually necessary to condense the incident beam by means of a lens in order to obtain detectable intensities of transmitted radiation. Thus the technique is more difficult and time-consuming than the familiar, routine solution measurement but it can provide much more information. 

Weinstock et al. " noted that the combination bands (P + pj) and ( 2+ s) appear with similar frequencies, intensities, and shapes in the infrared spectra of MoFcfd ) and RhF< (if ). As is shown in Fig. 11-16, however, ( 2+ 3) was very broad and weak in TcF (d ), ReFfefi/ ), RuFfe(rf ), and OsFt,(d ). This anomaly was attributed to a dynamic Jahn-Teller effect. The static Jahn-Teller effect does not seem to operate in these compounds since no splittings of the triply degenerate fundamentals were observed. Perhaps the most fascinating... 

Very small samples can be analyzed by placing a ceramic (or other) standard between the sample and the cell cover. In this way, spectra have been recorded from samples as small as 10 )ul of liquid and a few milligrams of solid material. It is possible to emphasize a spectral anomaly (Woods anomaly) that occurs around 1500 nm if the surface presented to the instrument is not uniform. This will appear as a band of varying intensity. 

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