Radiation chemistry of overirradiated aqueous solutions of hydrogen cyanide and ammonium cyanide

Summary The radiolysis of aqueous solutions (O₂-free) of HCN and NH₄CN was examined at very large doses of⁶⁰Co gamma radiation (up to 230 Mrad). In this dose range the cyanide initially present (0.12 M) is decomposed and only its radiolytic products participate in the radiation-induced chemical process. It has been found that the weight of the dry residue containing the mixture of nonvolatile radiolytic products increases as doses increase up to 40 Mrad (up to about 4 g/l), but with further dose increases remains practically unchanged (NH₄CN) or decreases slightly (HCN). Carboxylic and amino acids are present in overirradiated samples. At increasing doses their concentrations decrease, with the exception of oxalic and malonic acids, which are continually produced and accumulate. This is also the case with the abundant NH₃ and CO₂, as well as with several other products that were generated at lower radiation-chemical yields. The molecular weights of the radiolytic products are up to 20,000 daltons throughout the dose range studied. Their amounts gradually change with increasing doses above 30 Mrad: The compounds with M_w between 2,000 and 6,000 daltons become more abundant, while the amounts of polymers with M_w between 6,000 and 20,000 decrease. The relevance of these findings for studies of chemical evolution is considered.