I'm trying to do some processing of optical emission spectra from sputtering plasmas, and am confused by what NIST means by 'easily reversed' in their notation. Anyone have a clue?
This means that the line in question can be apparent or not depending on whether the spectrum has been absorbed for other reasons. Or as Wikipedia states:
...the reabsorption near the line center may be so great as to cause a self reversal in which the intensity at the center of the line is less than in the wings.
Also, there is a paper that takes this topic more in depth: Effect of Self-Reversed Spectral Lines and the Temperature of the Switching Arc Plasma