Significance of both polarizability and polarizing power of cations in nitrate vibrational spectra

Vibrational frequencies of the NO3− ion in matrix‐isolated monomers of several nitrates MNO3 are shown to correlate with the polarizing power of the cation M+, P≡ (z/r)/Seff, properly defined as the quotient, rather than the product, of the ionic potential, z/r, and a factor Seff= (5z1.27)/(r(1/2)I) (Ahrens, 1954) representing the efficiency with which the electron shell of the cation screens its nuclear charge. For molten nitrates MNO3, this correlation breaks down: in the condensed state, the polarizability of the cation, a, becomes important as the result of the mutual enhancement of the polarization of a given cation by several anions. A correlation of ν1 with the product of cation polarizing power and polarizability, P a, is presented.