A case of @S05578@, when a line is self-absorbed to such an extent that the peak or central @W06659@ intensity is less than at the wings or non-central wavelengths.
Source: Orange Book, 2nd ed., p. 122 [Terms] [Book]
Cite as: IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). Online version (2019-) created by S. J. Chalk. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook.