Basic spectrometry: Collisional line broadening
 

For atoms which are radiating in an environment subject to a high pressure, the energy levels of the radiating or absorbing atom may be influenced by local charged particles (ions and electrons). In a gas, such perturbations are random and give rise to a broadening of the line—the Stark effect. There will be a high probability that the radiating atoms will suffer collisional impacts with adjacent atoms during the time interval of the individual emissions. As a result, the frequency associated with the emission will be blurred. Overall, the assembly of radiating atoms provides spectral line profiles which are broadened by the process according to the local density or pressure.