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Ultrafast energy redistribution in fullerenes: A real time study by two-color femtosecond spectroscopy
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View: Figures


Image of FIG. 1.
FIG. 1.

Illustration of energy redistribution processes in laser-excited fullerenes monitored in the present work with two-color pump-probe spectroscopy (for details see text).

Image of FIG. 2.
FIG. 2.

Mass spectra [ion yield as a function of mass/charge ratio in u] after interaction with blue (399 nm, ) and/or red (797 nm, ) laser pulses. (a) Only the blue pulse is active; (b) the red pulse leads, blue follows, ; (c) blue pulse leads (pump), red follows (probe), corresponding to maximum signal; and (d) only the red pulse is active. Note the break in the ion signal scale between 0.18 and 0.2 arbitrary units, followed by different scalings. Similarly the mass scale is broken between u and 650 u. The small insets for the fragments illustrate that these signals are extremely weak.

Image of FIG. 3.
FIG. 3.

Expanded scale for a section of the mass spectra in Figs. 2(b) and 2(c) illustrating the mass resolution and showing metastable decay (peaks marked by ) into fullerenelike fragments . Otherwise as Fig. 2. Note again the break in the ion signal scales and the different scales. The ion yields for are approximately ten times larger than for !

Image of FIG. 4.
FIG. 4.

Total ion yield for different charge states as function of the time-delay between 399 nm pump and 797 nm probe pulse . At positive delay times the blue pulse comes first, the red follows, while the opposite holds for negative delay times. Zero delay, determined from MPI in Xe (see text), is indicated by the vertical black dashed line. The transient ion signals are fitted (full black line) with individual contributions indicated in the legend and described in the Appendix.

Image of FIG. 5.
FIG. 5.

Total ion yield for different fragments as function of the time delay between 399 nm pump and 797 nm probe pulse. Otherwise as Fig. 4.

Image of FIG. 6.
FIG. 6.

Relative yield of metastable fragment ions for the doubly charged fragments and as function of delay time, as derived from data illustrated in Fig. 3. Here, all measured signals have been smoothed over five data points in order to reduce statistical noise. The lines are simple sigmoidal fits to guide the eyes.

Image of FIG. 7.
FIG. 7.

Relaxation times for highly excited electrons due to electron-electron and electron-vibratonal couplings as determined from fitting the transient signals shown in Figs. 4 and 5. The results are presented in this graph in analogy to the mass spectra in Fig. 2, i.e., for fragments (open symbols) are ordered from to the left side of the respective parents (full symbols). Two sets of data for different pump and probe pulse intensities ( and , respectively) have been evaluated as noted in the legend. The dotted line (with error bar) indicates the electronic relaxation time for derived in previous studies (see text), while the dashed and dash-dotted lines are drawn to guide the eyes. Note that the values of derived from the transients of different photoions and fullerenelike fragments refer to the respective neutral precursor molecules.

Image of FIG. 8.
FIG. 8.

(a) Ratios and of additional ion yields from highly excited and thermalized medium energy electrons to the red only signal according to the scheme in Fig. 1 as derived from Figs. 4 and 5. These ratios can only be given for the more intense red laser pulse since with the weaker red laser pulse the red only signal vanishes. (b) Ratios of ion yields from highly excited to those from thermalized, medium energy electrons. Otherwise as Fig. 7.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Ultrafast energy redistribution in C60 fullerenes: A real time study by two-color femtosecond spectroscopy