different between absorptivity vs absorptance

English

absorptive +? -ity

absorptivity (plural absorptivities)

The quality of being absorptive; absorptiveness. [First attested in the mid 19^th century.]
(thermodynamics) The fraction of radiation absorbed by a surface to the total radiation incident on the surface. [First attested in the mid 19^th century.]
(analytical chemistry) The constant a in the Beer's law relation A = abc, where A is the absorbance, b the path length, and c the concentration of solution. Also known as absorptive power. Formerly known as absorbency index; absorption constant; extinction coefficient.

Circa 20th century, from absorption +? -ance.

(Received Pronunciation) IPA^(key): /?b?z??p.tn?s/
(US) IPA^(key): /æb?s??p.tn?s/, /æb?z??p.tn?s/, /?b?s??p.tn?s/, /?b?z??p.tn?s/, IPA^(key): /æb?s??p.tn?ts/, /æb?z??p.tn?ts/, /?b?s??p.tn?ts/, /?b?z??p.tn?ts/

absorptance (plural absorptances)

(optics, physics) Absorbed radiation and incident radiation in a ratio format; a measurement that shows how well a surface absorbs radiation. [First attested in the mid 20^th century.]