Dissociation energies of alkali metal cyanides

Equilibrium constants for the reaction M ÷ HCN ⇌ MCN + H, where M is an alkali metal atom have been determined by measuring the effect of added C 2 N 2 on the intensity of emission of metallic resonance lines from a fuel-rich, pre-mixed H 2 /N 2 /O 2 flame at 1500 K. The yield of HCN from the cyanogen was measured by withdrawing samples through a quartz micro-probe for mass spectrometric analysis. The enthalpy change of the reaction was calculated by the third-law method. We find D MCN o to be 497, 474, 497, 487, and 501 kJ mol −1 for M  Li, Na, K, Rb, and Cs, respectively, all ± 22 kJ mol −1 .