An ab Initio Study on the Equilibrium Structure and XCN Bending Energy Levels of Halofulminates: ClCNO

The molecular parameters of chlorofulminate, ClCNO, were determined in large-scale ab initio calculations using the coupled-cluster method, CCSD(T), and basis sets of double- through quintuple-zeta quality. With the largest basis set employed, the equilibrium structure of the molecule was found to be bent, with the parameters r (ClC) = 1.6490 Å, r (CN) = 1.1749 Å, r (NO) = 1.2039 Å, ∠(ClCN) = 152.22°, and ∠ (NCO) = 171.50°. The potential energy function for the large-amplitude ClCN bending motion (the ν 5 mode) was determined to be strongly anharmonic, with a barrier to linearity of the ClCNO chain of 156 cm -1 . The rotation−bending energy levels were then calculated using a semirigid-bender Hamiltonian. The effective rotational constants determined for various ν 5 states were found to be in excellent agreement with the recent experimental data.