Response of Polyatomic Molecules to Ultrastrong Laser- and Ion-Induced Fields

The exposure of molecules to short, ultrastrong electric fields leads to multiple ionization and a subsequent Coulomb explosion. We present a comparative study where uracil molecules are exposed to fields generated by high-power laser pulses ($\tau \approx 75\mathrm{fs}$, $I>{10}^{16}\mathrm{W}/{\mathrm{cm}}^2$) or swift highly charged ions (0.5 MeV ${\mathrm{Xe}}^{25+}$) representing a half-cycle pulse of less than 10 fs duration. Molecular dynamics and structural information contained in the fragmentation pathways can be assessed separately. Despite the similar field strengths large differences in fragment kinetic energies are found which are related to field shape and duration with the aid of molecular dynamics simulations.

Figure 1

Mass spectra of uracil fragment cations induced by ${\mathrm{Xe}}^{25+}$ ions [0.5 MeV, (a)] and laser pulses [$\tau \approx 75\mathrm{fs}$, $I\le 5\times {10}^{16}\mathrm{W}/{\mathrm{cm}}^2$, polarization parallel to the detection axis, (b)].

Figure 2

Kinetic energy distributions for ${\mathrm{O}}^{q+}$ (top), ${\mathrm{N}}^{q+}$ (middle) and ${\mathrm{C}}^{q+}$ (bottom). Left: interaction with 0.5 MeV ${\mathrm{Xe}}^{25+}$, right: laser ($\tau \approx 75\mathrm{fs}$, $I\le 5\times {10}^{16}\mathrm{W}/{\mathrm{cm}}^2$).

Figure 3

Kinetic energy distributions for ${\mathrm{O}}^{q+}$ (top), ${\mathrm{N}}^{q+}$ (middle) and ${\mathrm{C}}^{q+}$ (bottom). Symbols: experiment, data from Fig. 2. dashed: simulation. (a) 0.5 MeV ${\mathrm{Xe}}^{25+}$, (b) laser ($\tau =150\mathrm{fs}$, $I=3.5\times {10}^{16}\mathrm{W}/{\mathrm{cm}}^2$).