Orientation and Composition Studies of Lignin in Woody Tissue

3 Orientation and Composition Studies of Lignin in Woody Tissue 

Developments in Raman spectroscopy and wood sampling techniques have made it possible to carry out in situ studies on the organization of lignin and 

At this time, Raman spectroscopic studies of lignin have just begun and the capability of the technique has not been fully realized. Work done so far indicates a great potential for the technique. Moreover, Raman spectroscopy is by no means a fully matured branch of spectroscopy and further development in this field is expected. 

The nature of the information that can be obtained from Raman experiments, namely, vibrational frequencies and band intensities, is similar but not identical to that of infrared spectroscopy. Therefore, it is appropriate to compare these two techniques. As mentioned previously, for a molecular vibration to be IR active, a change in dipole moment accompanying the vibrational transition is 

Ordinary Raman scattering is an inefficient process, and in general it is less sensitive than IR absorption. However, in certain lignin samples, conjugation, resonance, or pre-resonance Raman effects can arise, and for particular vibrational modes a higher level of sensitivity can be achieved (Long 1977, Schmid and Brosa 1971). In lignins, the latter effect can be induced by proper laser frequency selection. 

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