A correlated ab initio study of linear carbon-chain radicals CnH (n = 2−7)

Linear carbon-chain radicals CnH for n = 2−7 have been studied with correlation consistent valence and core-valence basis sets and the coupled cluster method RCCSD(T). Equilibrium structures, rotational constants, and dipole moments are reported and compared with available experimental data. The ground state of the even-n series changes from 2Σ+ to 2Π as the chain is extended. For C4H, the 2Σ+ state was found to lie only 72 cm−1 below the 2Π state in the estimated complete basis set limit for valence correlation. The C2H− and C3H− anions have also been characterized.