Re: 'How can bond strengths be determinated by means of IR spectroscopy?

Spectroscopy is the study of the interaction of electromagnetic radiation 
with a chemical substance.  The frequencies that these substances will 
absorb are unique for each molecule.  Generally, the wavenumber is used to 
measure the position of an infrared (IR) absorption.  IR absorption bands 
are common in most organic and inorganic compounds.   When IR light in 
incident on the molecule, the frequency, which matches the natural 
frequency of that molecule, is absorbed resulting on molecular 
vibrations.   These vibrations can either be stretching or bending.   As 
only a few molecules also exhibit rotation transitions upon IR absorption 
the vibrational transitions are of more practical interest.

For diatomic molecules:

v = 1/(2*pi*c) * sqrt{[k(m1+m2)]/(m1*m2)}

Where, v = the wavenumber [cm-1], pi = 3.1415926…, c = speed of light in a 
vacuum [cm/s], k = the force constant [dynes/cm], and m1 & m2 are the 
masses of the vibrating atoms within the molecule [g].

The force constant (k) is proportional to the bond energy for stretching 
and the overall resistance to motion for bending. Specific vibrational 
wavenumbers can be observed from any IR absorption spectrum.  By knowing 
these wavenumber and the molecule (atoms) involved in the scan, the 
previous equation can be solved for the force constant.

Following are several additional references related to IR spectroscopy and 
bond strength:
www.scar.utoronto.ca/~jthompso/chmc31/c31irtes.pdf 
chemlearn.chem.indiana.edu/c343/08-C343IR.pdf 
willson.cm.utexas.edu/Teaching/Chem618B/Files/PDF_Lectures/ lecture6.pdf 
www.vuw.ac.nz/scps/students/chem206/c206spectroscopy.pdf