multipole line

in X-ray spectroscopy
https://doi.org/10.1351/goldbook.M04064
See: selection rule
Source:
PAC, 1991, 63, 735. 'Nomenclature, symbols, units and their usage in spectrochemical analysis - VIII. Nomenclature system for X-ray spectroscopy (Recommendations 1991)' on page 738 (https://doi.org/10.1351/pac199163050735)