Pressure broadening
= Pressure broadening
{title2=$\Delta\nu\sim\Gamma/(2\pi)$}
Collisions and fluctuating neighboring-particle electric fields alter atomic energy levels and coherence times, broadening a <spectral line>. In a simple impact treatment the coherence-decay rate gives a Lorentzian width of order $\Gamma/(2\pi)$; the precise definition of full or half width must be stated. Unlike <Doppler broadening>, this depends primarily on collision rates and perturber density. In stellar <opacity> calculations it alters line overlap and the low-opacity windows entering the <Rosseland mean opacity>.