An efficient method for coupled rotation and torsion of oriented AXn1–BYn2 molecules with application to BF2BCl2

A new and concise method to obtain the eigenvalues and eigenfunctions of a two-dimensional rotational-torsional Hamiltonian with correct boundary conditions is proposed for oriented AXn1-BYn2 type molecules. The corresponding eigenfunctions are not only eigenfunctions of the Hamiltonian but also common eigenfunctions of several symmetry operators. Numerical calculations for the lowest 1000 rotational-torsional eigenstates of BF2BCl2 demonstrate the advantages and applicability of our method.