Knowledge Bank

On the basis of large-scale open-shell coupled cluster calculations accurate equilibrium structures are established for a number of molecules in triplet ground states. Among these are species of type $HC2nN(n=1-3)$, $C2nS(n=1-3)$, $SiC2n+1(n=1-3)$ and $SiC2n-1S(n=1-4)$. The equilibrium structure of $HC2N$ is definitely non-linear with a barrier height to linearity close to $300cm-1$. On the other hand, triplet HC4N has a linear equilibrium structure and this probably also holds for the larger members of the series. Various spectroscopic properties calculated for the above mentioned molecules are discussed.