AbstractThe Raman spectra of gaseous hydrazine and hydrazine‐d4have been recorded from 40 to 3500 cm−1. For the ‘light’ molecule, strongly polarized lines at 3398, 3329 and 1076 cm−1have been assigned to the NH antisymmetric stretch, NH symmetric stretch, and NN stretch, respectively. For the hydrazine‐d4molecule, strongly polarized lines at 2442, 2422, 1031, 930 and 749 cm−1have been assigned to the ND antisymmetric stretch, ND symmetric stretch, NN stretch, ND2was and ND2rock, respectively. The Raman spectra of both solid hydrazine and hydrazine‐d4have been recorded and the splitting in the intramolecular fundamental region indicates that there are at least four molecules per primitie cell. In the lattice region of the spectra the optical translations and librations are assigned and the number of lattice modes rules out both of the space groups previously proposed for hydrazine from sca