ln() (crosses), ln() (circles) and ln() (triangles) as a function of the inverse of the temperature. , and are the rates for the HNCO + NH₃ → NH₄⁺ + OCN⁻ reaction using a rate equation approach, a Monte Carlo approach, and a gamma distribution approach, respectively. The uncertainty on a point is given by the dispersion of the measurements at 20 K. The dashed lines represent the fit of the experimental points against an Arrhenius law for each approach.