Neutron-rich light nuclei and their reactions play an important role for the creation of chemical elements. Here, data from a Coulomb dissociation experiment on $^{20,21}$N are reported. Relativistic $^{20,21}$N ions impinged on a lead target and the Coulomb dissociation cross section was determined in a kinematically complete experiment. Using the detailed balance theorem, the $^{19}mathrm{N}(mathrm{n},gamma)^{20}mathrm{N}$ and $^{20}mathrm{N}(mathrm{n},gamma)^{21}mathrm{N}$ excitation functions and thermonuclear reaction rates have been determined. The $^{19}mathrm{N}(mathrm{n},gamma)^{20}mathrm{N}$ rate is up to a factor of 5 higher at $T<1$,GK with respect to previous theoretical calculations, leading to a 10,% decrease in the predicted fluorine abundance.
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