The equilibrium geometry and some spectroscopic constants of C5 from large-scale ab initio calculations

An accurate equilibrium geometry for linear C5 (X̃ 1Σ+g) has been obtained from coupled-cluster single, double, and triple [CCSD (T)] calculations (all electrons correlated) with a large basis set of 275 contracted Gaussian-type orbitals: R1e (outer CC)=1.289 59 Å and R2e (inner CC)=1.281 90 Å. Analogous calculations for C3 and C2 in their electronic ground states yield 1.294 31 and 1.242 09 Å, respectively. The equilibrium dissociation energy C5→C3+C2 is predicted to be 597 kJ mol−1.