Figure (right) reports the S 1 adiadatic population for the 2D, 2D + 1BM and 2D + 2BM, 2D + 6BM and 2D + 23BM models and, as for the diabatic populations, the bath modes have a small effect on the populations. The fast oscillations observed up to 150 fs in the diabatic populations are absent in the adiabatic populations. Such small oscillations arise from the non-zero nonadiabatic coupling contributions around the initial diabatic wavepacket; the corresponding initial adiabatic wavepacket is slightly delocalized on the S 0 adiabatic state and its initial S 0 population is about 0.3 %. This delocalization creates population oscillations with a corresponding period, τ 1 (τ 1 = 1.67 f s), associated to the energy difference between the two diabatic states or to the parameter E 1 of the model (see Section IV).