Below you will see the infrared spectrum of water's complex refractive
index as measured by 4 different groups. Notice how the real
part of refractive index varies fairly dramatically at some wavenumbers,
and that the imaginary part is fairly similar.
The infrared spectral properties of water cloudsdepend strongly on the complex refractive index.
Each group apparently turns the Kramers Kroenig crank a little differently
in deriving the real part from the measured imaginary part, perhaps explaining
the variation. Or perhaps we all drink from a different cup?

Real part of the refractive index of water as determined
by 4 different groups.

Imaginary part of the refractive index of water as determined
by the 4 different groups defined in the real part figure. Note the similarity.