Vibrational spectroscopy at very high pressures. Part 22.—Raman study of sodium and potassium cyanides

Abstract

Raman Spectra of KCN have been investigated up to ≈ 55 kbar and NaCN to ≈ 37 kbar, KCN (III) shows no distinct lattice mode spectrum and, in this respct, is similar to cubic KCN (I), KCN(IV) shows only a broad doublet, interpreted as due to both libratory and translatory motions, but distinguished from the behaviour of the B1-related phases in being at much higher frequency. The behaviour of the single _ν(CN) band found for each phase has been studied as a function of pressure values of d_ω/dP(cm^–1kbar^–1) are : KCN (I) at 20°C, 0.50; KCN (I) at 110°C, 0.57₄; KCN (III) at 110°C, 0.45; KCN (IV) at 20°C, 0.32.

Results for NaCN confirm those recently reported for pressures up to 6 kbar but extend them to much higher pressures. For NaCN (II) d_ω/dP(cm^–1kbar^–1) is 0.57 up to 21 kbar but is reduced to 0.45 above that pressure. There is a similar change of slope at 21 kbar in the frequency against pressure plot for the two low-frequency bands but this is thought not to have structural significance.