

Spectra
lines have a position and a height. The position of lines has been
described as the separation of energy levels. The next section will
attempt to give meaning to the intensity of spectral lines.
Go back to Applet 1.
The intensity of spectral lines is determined by the relative probabilities
transitions between various energy levels. Selection rules for rotational
Raman allow only J=±2.
Q4.1 The intrinsic probability for a transition of a single molecule
from J = 0 to J = 2 is the same as that for a transition from J =
1 to J = 3. Why are not all spectral lines equally intense?
Q4.2 What is the relationship between the intensities of the Stokes
and AntiStokes lines? Explain this in terms of the population of
the energy levels.
The reason that the intensity of the spectral lines tail to zero is
the influence on populations of an exponential term: 