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So far we have studied standard spectroscopic methods involving transitions amongst molecular rotational, vibrational, electronic and nuclear and electron spin energy levels. There are several other techniques, as well as newly emerging methods which enable one to study other details of molecules as well as allow us to study molecules as a function of time, i.e., as a molecule goes from one state to another. Time resolutions of a femtosecond 10-15s have been accomplished. The development of pulsed lasers has contributed phenomenally to this progress. In the present lecture we shall explore a few more spectral techniques so as to see which other aspects of molecular behaviour can be probed. Some topics covered in this lecture are Mossbauer spectroscopy, nuclear quadrupole resonance (NQR) spectroscopy, Raman spectroscopy, mass spectroscopy/spectrometry. X ray crystallography or mass spectroscopy do not strictly involve transitions between molecular energy levels. Nevertheless, they give complementary useful information on the structure of molecules. |
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Mossbauer spectroscopy involves the absorption of γ - rays (photons of frequency 1019 Hz or wavelengths of 10 pm). The method uses the Mossbauer effect which is the recoilless emission and resonant absorption of γ - rays. A typical energy level diagram involved in a Mossbauer spectrum and a block diagram of the corresponding spectrometer is shown below: |
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a) Energy levels b) Mossbauer spectrometer
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Figure 15.1. Energy levels (a) and a block diagram (b) for Mossbauer spectroscopy |
