HCNO AS A SEMIRIGID BENDER

The semirigid bender Hamiltonian [Bunker and Landsberg, J. Mol. Spectrosc., 67, 374-385 (1977)] is used to fit the rotation-vibration energy level separations in the fulminic acid (HCNO) molecule. The allowance made in the model for the variation of the CH and CN bond lengths with the HCN bending angle proves to be very important, and as well as achieving a good fit we are able to make a detailed investigation of the shape of the HCN bending potential function. From the results we conclude that the equilibrium structure of HCNO is linear but that excitation of the ν1 or ν2 stretching vibrations gives rise to an effective HCN bending potential function having its minimum at a nonlinear configuration. Even in the ground state the zeropoint vibrational contributions from ν1 and ν2 to the effective HCN bending potential give a small barrier (11.5 cm-1) to linearity, and we determine that the zero-point HCN bending vibrational amplitude is ±34°. © 1979.