Fig. 4: Time-dependent fragmentation channels.

a The C₃H\({}_{x}^{+}\) momentum profile formed from FLU as a function of XUV-IR laser pulse delay. The IR pulse interacting with the molecular beam before the XUV pulse gives negative pump-probe delay values, whereas for positive pump-probe values, the XUV pulse interacts first. The vertical black dotted line indicates t₀ determined by the helium electron sidebands. Channels and numbered features are described in detail in the text. Briefly, (1) and (2) show the increase in C₃H\({}_{x}^{+}\) ions formed by dissociative ionization from the PAH³⁺ and PAH²⁺ ion, respectively, around t₀. (3) shows the increase in C₃H\({}_{x}^{+}\) ion signal after t₀ due to the XUV pulse creating PAH⁺ ions that are dissociated by the IR pulse. (4) and (5) show the increase in signal in the (1, 1) and (1, 0) channels following relaxation of the PAH²⁺ and PAH⁺ ions, respectively, and dissociation by the IR laser pulse. (6) highlights the general increase in signal after t₀ compared to before t₀, even after a long pump-probe delay, in this case, due to the XUV pulse creating PAH²⁺ ions which are dissociated by the IR pulse. White arrows highlight the shift in channel yields from pathway β and γ to pathway δ, as denoted in (b). b Schematic of the PAH states involved in this experiment. Solid black lines and dashed lines represent bound and dissociative electronic states, respectively. Blue and red arrows represent the effects of the XUV laser and IR laser pulses, respectively. The pump pulses are able to populate a multitude of electronic states, as represented by the blue and red shaded areas for the XUV and IR pulses, respectively. Electronic relaxation of the wavepacket over time is represented by the curvature in the shaded areas. The change in electronic states due to relaxation alters the product of the probe pulse. c Integrated plots of the (1, 0), (1, 1), and (1, 2) channels from (a). Plots are normalized to the maximum signal detected in the (1, 1) channel, and t₀ is represented by the dotted black line.