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 co rrelation consistent valence and core-valence basis sets and the coupl ed cluster method RCCSD(T). Equilibrium structures, rotational constan ts, and dipole moments are reported and compared with available experi mental data. The ground state of the even-n series changes from (2) Si gma(+) to (2) Pi as the chain is extended. For C4H, the (2) Sigma(+) s tate was found to lie only 72 cm(-1) below the (2) Pi state in the est imated complete basis set limit for valence correlation. The C2H- and C3H- anions have also been characterized.