A pseudo-spectral algorithm for the computation of transitional-mode eigenfunctions in loose transition states

An algorithm is presented for the exact action of the Hamiltonian describing the interfragment motions in a loose transition state. The working basis set consists of body-fixed Wigner functions, in terms of which the rotational kinetic energy operator is almost diagonal. The action of the potential operator is effected by transformation to a discrete variable representation. Eigenfunctions and eigenvalues corresponding to the exact adiabatic channel potentials can be obtained using the Lanczos algorithm. Illustrative calculations are presented for the dissociation of ketene into singlet methylene and carbon monoxide fragments. The algorithm is tailored to deal with very large basis sets.