Control of rotational wave-packet dynamics in asymmetric top molecules

We combine newly developed experimental and theoretical methods to explore and control the rotations of asymmetric top molecules. In the low-temperature limit, the revival spectra of laser-driven rotational wave packets exhibit a fascinating quantum-mechanical structure, which is qualitatively different for asymmetric tops compared to symmetric or linear tops. With increasing fluence, the structure gradually simplifies, illustrating a controllable transformation of the rotational dynamics. Our theoretical and experimental predictions are in qualitative agreement.

Figure 1

(Color online) Computed revival spectra for an asymmetric top molecule vs the dimensionless time parameter $\overline{t}=(\hslash ∕\overline{I})t$. The three columns are obtained for $\kappa =-0.965$ (left), $-0.90$ (middle), and $-0.80$ (right). $T_{\mathrm{rot}}=0.4\mathrm{K}$ and ${\tau }_{\mathrm{align}}=0.71\mathrm{ps}$. The fluences (peak intensities) in the upper, middle, and lower rows are $0.14\mathrm{J}∕{\mathrm{cm}}^2$ $(2\times {10}^{11}\mathrm{W}∕{\mathrm{cm}}^2)$, $0.71\mathrm{J}∕{\mathrm{cm}}^2$ $(1\times {10}^{12}\mathrm{W}∕{\mathrm{cm}}^2)$, and $4.2\mathrm{J}∕{\mathrm{cm}}^2$ $(6\times {10}^{12}\mathrm{W}∕{\mathrm{cm}}^2)$, respectively. The arrows mark the positions of the $C$-type revivals (see text).

Figure 2

(Color online) ${\mathrm{I}}^{+}$ ion images obtained (a) without the alignment pulse, and (b), (c) with a 0.2-ps-long alignment pulse $(F_{\mathrm{align}}=3.3\mathrm{J}∕{\mathrm{cm}}^2)$. In (b) the molecules align at $t=351.0\mathrm{ps}$, corresponding to the maximum of the half $J$-type revival. In (c) the molecules anti-align at $t=702.0\mathrm{ps}$ corresponding to the minimum of the full $J$-type revival. The probe and alignment pulses are polarized perpendicular and parallel (vertical) to the image plane. The circular rings mark the (${\mathrm{I}}^{+}$, ${\mathrm{C}}_6{{\mathrm{H}}_5}^{2+})$ channel (see text).

Figure 3

$⟨{\cos }^2{\theta }_{2D}⟩$ recorded in three time intervals representing the rotational dynamics shortly after the alignment pulse and in the two first regions with $J$-type and $C$-type revivals. The measurements are carried out at four different fluences and pulse durations, indicated on each panel. The peak intensities are (a) $1.6\times {10}^{13}$, (b) $1.1\times {10}^{13}$, (c) $8.5\times {10}^{12}$, and (d) $5.9\times {10}^{12}\mathrm{W}∕{\mathrm{cm}}^2$. In the absence of the alignment pulse $⟨{\cos }^2{\theta }_{2D}⟩=0.5$. Each data point is obtained from an ${\mathrm{I}}^{+}$ image accumulated over 1500 laser shots and containing $\sim 40000$ ion hits.

Figure 4

Computed revival spectra of iodobenzene immediately after the alignment pulse and in the vicinity of the first and second revivals at four different fluences and durations (indicated on each panel). $T_{\mathrm{rot}}=1.0\mathrm{K}$ and the peak intensities are (a) $8.0\times {10}^{12}$, (b) $5.5\times {10}^{12}$, (c) $4.4\times {10}^{12}$, and (d) $3.1\times {10}^{12}\mathrm{W}∕{\mathrm{cm}}^2$.