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=ea ax1(x1)! 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]