Abstract
The free energy function, heat content and heat capacity of cyanogen and the cyanogen halides, ClCN, BrCN and ICN, have been calculated for a series of temperatures from spectroscopic and electron diffraction data. Since no experimental value for the carbon‐iodine distance has been as yet obtained, an extrapolation is made from the values for the carbon‐chlorine and carbon‐bromine distances in the corresponding cyanogen compounds. 1.96±0.04A is obtained for the I–C distance in cyanogen iodide. The free energies of formation of gaseous (CN)2, ClCN and ICN have been calculated from thermal and equilibrium data. The values of ΔF°298.1 are, 69.1 kcal./mole for (CN)2, 35.5 kcal./mole for ClCN, and 46.75 kcal./mole for ICN. It is estimated that for gaseous BrCN ΔF°298.1=40 kcal./mole.

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