Vibrational modes

Vibrational modes in ionic crystals

The lattice vibrations of ionic crystals which are accompanied by large dipole moments are a classical example in far infrared spectroscopy, too. The example below shows the reflectivity of a thick KBr sample illuminated by p-polarized light (65° angle of incidence) - once again the measurement is plotted in red and the simulation in blue.

The spectrum features the very strong transverse optical phonon and on its right shoulder some structures due to multiphonon absorption. All excitations can be described well by harmonic oscillators whose parameters have been adjusted in the fit. The list below is a screen copy of the SCOUT object defining the dielectric function:

Each harmonic oscillator contribution has a name, a resonance frequency position (denoted by Pos.), an oscillator strength (Str.) and a damping constant (Damp.).
The dielectric function that results from the parameter fit is shown here (blue: real part, red: imaginary part):

SCOUT_98 users: This example is available as configuration file that you can download

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