Poisson distribution 

https://doi.org/10.1351/goldbook.P04707
A discrete distribution with the differential mass-distribution function of the form: fw(x)=xa+1=e−a ax−1(x−1)! where x is a parameter characterizing the chain length, such as relative molecular mass or degree of polymerization and a is a positive adjustable parameter.
Source:
Purple Book, 1st ed., p. 56 [Terms] [Book]
Citation: 'Poisson distribution' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.P04707 RIS BibTex EndNote
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Last revised: February 24, 2014