self-reversal

https://doi.org/10.1351/goldbook.S05586
A case of self-absorption, when a line is self-absorbed to such an extent that the peak or central wavelength intensity is less than at the wings or non-central wavelengths.
Source:
Orange Book, 2nd ed., p. 122 (https://media.iupac.org/publications/analytical_compendium/)