absolute activity, λ

The exponential of the ratio of the chemical potential, $μ$ , to $R T$ where $R$ is the gas constant and $T$ the thermodynamic temperature, $λ = e μ R T$ .

Source:

Green Book, 2nd ed., p. 40

See also:

PAC, 1984, 56, 567 (Physicochemical quantities and units in clinical chemistry with special emphasis on activities and activity coefficients (Recommendations 1983)) on page 569
PAC, 1996, 68, 957 (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 959