Torsional-Rotational Dynamics of Carbodiimide, HNCNH: A Semirigid Bender Approach

Abstract A one-dimensional semirigid bender Hamiltonian was developed for the description of the torsional motion of carbodiimide, HNCNH. The interaction of torsion with the other vibrational degrees of freedom is described by the variation of molecular geometry along the minimum energy torsional tunneling path. The large changes of the ∠HNC angles during torsion generate rotationally dependent contributions to the effective torsional potential function, which explain qualitatively the observed decrease of the torsional splittings as a function of K a in the rotational spectrum of the ground torsional state. The parameters of the minimum energy torsional path were optimized with respect to the available experimental splittings and rotational constants and used for predictions of rotational constants and torsional splittings of the first excited torsional state of HNCNH as well as the ground and first excited torsional states of DNCND.