Bandshapes of H-Bonds Fermi Resonances

Another mechanism also often appears in the bands of H-bonded systems. It has been put into evidence in dimers of acetic acids (22), where the wavenumbers of various submaxima 

Infrared Spectroscopy of H-Bonded Systems Theoretical Descriptions 

Fermi resonance does not modify the integrated intensity of the 0 - 1 transition in q, and it can be shown that it neither modifies the wavenumber of its centre. The appearance of a doublet instead of a singlet shows that it modifies its width. The presence of a Fermi resonance starts having an effect only on the moments of order higher than 1, that is on the width and shape of the band in q, but it has no effect on its first two moments. 

In this appendix we briefly sketch, withont any demonstration and with the minimum of mathematical formula, some basic aspects of IR spectroscopy that are invoked all along this book. We first define some mathematical but nevertheless simple notations that are cnrrently nsed in qnantnm physics because they avoid heavier writing with integrals. Thus, an integral quantity that implies two vibrational wavefunctions and and an operator that may be a fnnction of a coordinate q, or a differential operator such as its conjugated momentum p, defined as 

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