AbstractPolarized infrared and Raman spectra of K2[RuCl5NO] and (NH4)2[RuCl5NO] have been obtained and a precise assignment of the four RuCl stretching modes has been made. The lower frequency vibration is unambiguously assigned to the axial RuCl stretch in agreement with previous findings based on substitution of the axial (transto the NO group) halogen ligand. The results are discussed in terms of Mössbauer data and population anal