Sreekanth,

Have a look at the Wikipedia article for the unit:

http://en.wikipedia.org/wiki/Wavenumber

"The historical reason for using this quantity is that it proved to be convenient in the analysis of atomic spectra. Wavenumbers were first used in the calculations of Johannes Rydberg in the 1880s. The Rydberg–Ritz combination principle of 1908 was also formulated in terms of wavenumbers. A few years later spectral lines could be understood in quantum theory as differences between energy levels, energy being proportional to wavenumber, or frequency. However, spectroscopic data kept being tabulated in terms of wavenumber rather than frequency or energy, since spectroscopic instruments are typically calibrated in terms of wavelength, independent of the value for the speed of light or Planck's constant."

Sreekanth,

Have a look at the Wikipedia article for the unit:

http://en.wikipedia.org/wiki/Wavenumber

"The historical reason for using this quantity is that it proved to be convenient in the analysis of atomic spectra. Wavenumbers were first used in the calculations of Johannes Rydberg in the 1880s. The Rydberg–Ritz combination principle of 1908 was also formulated in terms of wavenumbers. A few years later spectral lines could be understood in quantum theory as differences between energy levels, energy being proportional to wavenumber, or frequency. However, spectroscopic data kept being tabulated in terms of wavenumber rather than frequency or energy, since spectroscopic instruments are typically calibrated in terms of wavelength, independent of the value for the speed of light or Planck's constant."

Dear Dr. William Weaver,

Thank you for an informative answer.

Sreekanth

It is a general feature in many cases to use alternative units when there is only constants involved between different magnitudes. For example, E=mc**2, you can use the mass as "energy", or the thermal energy E=kb* T, you can use the temperature scale as "energy", when the energy is related to light speed or Boltzmann constant

Raman shifts are typically reported in wavenumbers, which have units of inverse length, as this value is directly related to energy

The wavenumber (cm-1) scale is in fact an energy scale, See the conversion factors for J or eV in the following table: http://users.mccammon.ucsd.edu/~dzhang/energy-unit-conv-table.html. Differently from the wavelength scale, the wavenumber scale is linear, which is convenient.

In short rearm....Spectroscopists prefer using wavenumber (in K, 1K=cm-1) in FTIR and Raman spectroscopies because it scales linearly with energy.