## internal absorptance, $$\alpha_{\text{i}}$$

https://doi.org/10.1351/goldbook.I03100
absorptance when surface effects and effects of the cuvette such as reflection losses are excluded.
Source:
Green Book, 2nd ed., p. 32 (https://dev.goldbook.iupac.org/files/pdf/green_book_2ed.pdf)