Molar Napierian absorption coefficient divided by the Avogadro constant.
\(\sigma_{\rm{net}} = \kappa/N_{\rm{A}}\).
Source:
PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 667 (https://doi.org/10.1515/pac-2019-0203)