Hello Felipe,

     Concerning nonlinearity of among the hydrogen isotopes, you might
want to look at a remarkable paper from 1932 by Walker Bleakney.

Phys. Rev. 41, 32–38 (1932)
A Search for Isotopes of Hydrogen and Helium.

The abstract is online at

http://prola.aps.org/abstract/PR/v41/i1/p32_1


            Sincerely,

            Frank Simpson


Novato, California