An ab initio study on the equilibrium structure and HCN bending potential energy function of fulminic acid

The molecular parameters of fulminic acid, HNCO, have been determined in large-scale ab initio calculations using the coupled cluster method, CCSD(T), and basis sets of double to quadruple zeta quality. With the largest basis set employed. cc-pVQZ, the equilibrium structure of the molecule was found to be slightly bent, with the parameters r(HC) = 1.0615 Å, r(CN) = 1.1648 Å, r(NO) = 1.2025 Å, ∠(HCN) = 165.13°, ∠(NCO) = 176.58°. The potential energy function for the large-amplitude HCN bending motion was determined to be anharmonic, with a barrier to linearity of the HCNO chain of only 7 cm−1.