The effective Hamiltonian for the coupling between inversion-torsion states of hydrazine

In the present paper, a procedure to calculate matrix elements of the group-theoretical Hamiltonian for hydrazine is described and explained in detail, and a complete set of rovibrational matrix elements responsible for interstate interactions is presented. The transformation properties of the framework functions under the symmetry operators of the double group G16(2) are explained in a simple way using the MS Excel spreadsheet.