A main shortcoming of the GBOM as applied to realistic systems is that it does not exhibit any anharmonicity in the potential energy surface. To probe the influence of anharmonic effects on computed lineshapes, we turn to the 1D Morse oscillator with the system Hamiltonian taking the following form: Ĥg (q, p) = p2 2 + D g [1e -αg q] 2 (A4) Ĥe (q, p) = p2 2 + D e [1e -αe(q-k) ] 2 + ∆. (A5)