It was found that the data for 200 to 420C could be described by:

D (cm2/s) = 5.22 x 10-3 exp[-9.56(kcal/g-atom)/RT]

Y.Ebisuzaki, W.J.Kass, M.O’Keeffe: Journal of Chemical Physics, 1967, 46[4], 1378-81