An ab initio study on the equilibrium structure and torsional potential energy function of carbodiimide

The molecular parameters of carbodiimide (HNCNH) have been determined in large-scale ab initio calculations using the coupled-cluster method (CCSD(T)) and the correlation-consistent basis sets of double- through quadruple-zeta quality. The effect of core-electron correlation on the structural parameters was investigated. The equilibrium structural parameters of the molecule were estimated to be r(CN)=1.2242 Å, r(NH)=1.0092 Å, ∠(NCN)=170.62°, ∠(CNH)=117.84°, and ∠(HN…NH)=89.18°. The potential energy barriers for the trans and cis conformers were determined to be nearly equal, with the values 2636 and 2556 cm−1, respectively. The calculated molecular parameters were found to be in good agreement with experiment.