Doppler line broadening

Infrared spectroscopy 100-1500 Intensity 1 of rotational lines of light molecules Boltzmann factor for rotational levels related to I Also Doppler line broadening useful, principal applications to plasmas and astrophysical observations, proper sampling, lack of equilibrium, atmospheric absorption often problems... 

The first important line broadening mechanism is Doppler line broadening. It results from the movement that emitting species make towards or away from the point of observation. The contribution to line broadening is ... 

This situation corresponds to the well-known saturation effect in the emission of most gas laser transitions, where, for the same reason, fewer upper-state molecules can contribute to the gain of the laser transition at the center of the doppler-broadened fluorescence line than nearby. When tuning the laser frequency across the doppler-line profile, the laser intensity therefore shows a dip at the centerfrequen-cy, called the Bennet hole or Lamb dip after W.R. Bennet who discovered and explained this phenomen, and W.E. Lamb 2) who predicted it in his general theory of a laser. 

Besides the uncertainty broadening just discussed, there are other causes of line broadening which make line widths generally considerably greater than the natural width (3.88). The Doppler effect causes an apparent change in radiation frequency for molecules with a component of velocity cobs in the direction of observation of the radiation. Different molecules have different values of cobs and we get a Doppler broadened line. 

For Doppler lines there is little broadening with increasing self-absorption whereas for lint s with a Lorentz distribution of frequencies, self-absorption leads to a marked broadening, especially at the wings of the line. 

Another effect is due to the vibration of atoms in solids. At room temperature, this vibration leads to a Doppler effect and line broadening of the order of D x 10 eV. 

Figure 10.2. Absorption of y-ray photons by free atoms E = excitation energy E = recoil energy D = line broadening by the Doppler effect.

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