Fig. 3: Trajectories obtained by semiclassical calculations in neutral CH₃I.

The trajectories are classified by the kinetic energy release in case of ionization to various final states: (a) trajectories that remain bound as CH₃I⁺, (b) trajectories with sufficient energy to produce I⁺, and (c) trajectories that lead to CH₃⁺. The colormap shows the number of trajectories contributing to the creation of the respective ions without considering ionization probabilities. Horizontal dashed lines indicate multiples of the central NIR photon energy (1.65 eV) and allow us to identify the number n of NIR photons required to reach the ionization threshold. Bottom panels (d–f): Solid lines show the number of trajectories leading to fragment i in the (n-1,n) energy region (see main text). The dashed line in (e, f) represents the results obtained by considering only trajectories ending in the I*(²P_1/2) channel (i.e., no transfer of population from the ³Q₀ to the ¹Q₁ state). The numbers indicate the number of NIR photons that must be absorbed in each case. For comparison, the experimental data are shown as a shaded area in the background, together with some of the individual contributions obtained from the fit (dotted lines), each normalized to a maximum of 1.