Abstract
Ultrafast dynamics of a molecular wave packet created by a strong 120-fs near-infrared (800 nm) laser pulse in iodine has been probed by synchronized 13.4-nm, 35-fs extreme-ultraviolet pulses delivered by the free-electron laser facility in Hamburg, FLASH. The kinetic energy release of the multiply charged ionic fragments reveals three essential steps of strong-field-induced molecular fragmentation dynamics: (i) The creation of I${}_{2}$${}^{2+}$ and (I${}_{2}$${}^{2+}$)${}^{*}$ molecular ions proceeds within (75 $\ifmmode\pm\else\textpm\fi{}$ 15) fs full-width-at-half-maximum. (ii) With the onset of the I${}_{2}$${}^{2+}$ fragmentation the probability to lose a further electron within the same optical laser pulse rises with increasing I${}^{+}$---I${}^{+}$ internuclear separation and reaches its maximum after $\ensuremath{\sim}$30 fs with respect to the pulse maximum. (iii) Charge separation into the I${}_{2}$${}^{2+}\ensuremath{\rightarrow}{\mathrm{I}}^{2+}+\mathrm{I}$ dissociative channel with an asymmetric charge distribution is completed after (121 $\ifmmode\pm\else\textpm\fi{}$ 22) fs.
Highlights
Intense light pulses can produce highly excited nonequilibrium states of matter within femtoseconds
Our finding shows that the temporal origin of the I22+ molecular cationic state is confined within the NIR pulse envelope in correspondence with the current understanding of the multielectron dissociative ionization mechanism [6,7,8,9], as discussed in Sec
We have studied the dynamics of a I22+ molecular wave packet excited by a strong 800-nm NIR pulse
Summary
Intense light pulses can produce highly excited nonequilibrium states of matter within femtoseconds (fs). Experiments [15,16] have shown that iodine can be ionized up to I213+, but due to much shorter pulse durations of ∼30 fs employed there, all charge states were effectively formed at internuclear separations less than Rcr. For the lightest diatomic molecular ion H2+ (and D2+) the enhanced ionization region was resolved experimentally at two critical internuclear separations [17], in agreement with theoretical predictions [7]. The XUV ionization with subsequent Auger decay provides a way to probe the current electron configuration within fragmenting molecules and to unveil three essential steps of strong-field-induced molecular fragmentation dynamics shown in Fig. 1: creation of a molecular ion (a), valence electron localization due to the onset of fragmentation (b), and charge separation (c). These new fragmentation channels can unambiguously be ascribed to the channels produced by the dissociative ionization in a strong NIR field
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