H-K8 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.890422\,\lambda^2}{\lambda^2 - 109.832} + \frac{0.220099\,\lambda^2}{\lambda^2 - 0.0247289} + \frac{1.04379\,\lambda^2}{\lambda^2 - 0.00657042}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[8.89 \times 10^{-7} + 2(1.59 \times 10^{-8})\,\Delta T + 3(-3.21 \times 10^{-11})\,\Delta T^2 + \frac{5.87 \times 10^{-7} + 2(4.31 \times 10^{-10})\,\Delta T}{\lambda - 0.197}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$