picture of HCN–(HCCH)4, keeping the overhead acetylenes coincident. There are only very small orientation changes. Fig. 3 shows the three lowest energy n ¼ 12 structures. Comparison of the HCN–(HCCH)12 clusters with the optimum (HCCH)13 cluster shows slight differences, with such differences being greatest among acetylenes that are the nearest neighbors to the HCN. In a rough sense, HCN takes the place of an acetylene into an otherwise pure acetylene cluster without significant structural alteration.