mean free path, \(\lambda\)

https://doi.org/10.1351/goldbook.M03778
The average distance a molecule travels between collisions. For a molecule, \(\lambda =(\sqrt{2}\ \pi \ n\ d_{\text{m}}^{2})^{- 1}\), where \(n\) is the number of molecules per unit volume and \(d_{\text{m}}\) is their mean diameter. For O2 at one atmosphere and \(25\ \mathrm{^{\circ} C}\), this distance is only \(9.7\times 10^{- 6}\ \mathrm{cm}\); at \(10^{- 6}\) atmospheres and \(25\ \mathrm{^{\circ} C}\) it is \(9.7\ \mathrm{cm}\). For an @A00176@ particle, the mean free path, \(\lambda _{\text{B}}\) in the @S06027@ region (see @S06028@) is given by: \(\lambda _{\text{B}}=\sqrt{\frac{3\ k\ T}{m}}\ m\ B\) where \(m\) is the mass of the particle, \(k\) is the @B00695@ (\(1.381\times 10^{- 23}\ \mathrm{J}\ \mathrm{K}^{- 1}\)), \(T\) is the temperature (\(\mathrm{K}\)) and \(B\) is the @M03955@.
Sources:
Green Book, 2nd ed., p. 56 [Terms] [Book]
PAC, 1990, 62, 2167. (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2201 [Terms] [Paper]