He measured a spectrum of dinitrogen in 1929 which provided the first experimental evidence that the atomic nucleus is not composed of protons and electrons, as was incorrectly believed at the time.

His colleagues included Oscar D'Agostino, Emilio Segrè, Edoardo Amaldi, Ettore Majorana and Enrico Fermi, as well as the institute's director Orso Mario Corbino.

In 1939 the advance of fascism and the deteriorating Italian political situation led him to leave Italy, following the example of his colleagues Fermi, Segré and Bruno Pontecorvo.

With Fermi he had discovered the key to nuclear fission, but unlike many of his colleagues, he refused for moral reasons to work on the Manhattan project.

After the discovery of Raman scattering by organic liquids, Rasetti decided to study the same phenomenon in gases at high pressure during his stay at Caltech in 1928–29.

[8][9] This result was difficult to understand at the time, however, because the neutron had not yet been discovered, and it was thought that the 14N nucleus contains 14 protons and 7 electrons, or an odd number (21) of particles in total which would correspond to a half-integral spin.

[4] The Raman spectrum observed by Rasetti provided the first experimental evidence that this proton-electron model of the nucleus is inadequate, because the predicted half-integral spin has as a consequence that transitions from odd rotational levels would be more intense than those from even levels, due to nuclear spin isomerism as shown by Herzberg and Heitler for dihydrogen.