Structures and stabilities of CaC₃ isomers

A theoretical study of CaC₃ species has been carried out. As a general trend, triplet states are found to be more stable than singlet ones for all isomers. The predicted global minimum is a rhomboidal species, 4t(³B₁), whereas another rhomboidal four-membered ring, 3t(³A₁), is predicted to lie quite close in energy (about 8.2 kcal/mol higher in energy at the G2(P) level). The corresponding singlet states, 3s(¹A₁) and 4s(¹A₁), lie about 11.5 and 13 kcal/mol, respectively, above the predicted global minimum. Therefore our calculations suggest that several species could be accessible to experimental detection.