Nonsequential and Sequential Fragmentation of $\mathrm{CO}_2{}^{3+}$ in Intense Laser Fields

We experimentally studied the three-body fragmentation dynamics of ${\mathrm{CO}}_2$ initiated by intense femtosecond laser pulses. Sequential and nonsequential fragmentations were precisely separated and identified for $\mathrm{CO}_2{}^{3+}$ to break up into ${\mathrm{O}}^{+}+{\mathrm{C}}^{+}+{\mathrm{O}}^{+}$ ions. With accurate measurements of three-dimensional momentum vectors of the correlated atomic ions and calculations of the high-level ab initio potential of $\mathrm{CO}_2{}^{3+}$, we reconstructed the geometric structure of $\mathrm{CO}_2{}^{3+}$ before fragmentation, which turns out to be very close to that of the neutral ${\mathrm{CO}}_2$ molecule before laser irradiation. Our study indicated that Coulomb explosion is a promising approach for imaging geometric structures of polyatomic molecules if the fragmentation dynamics can be clearly clarified and the appropriate dissociation potential is provided for multiply charged molecular ions.

Figure 1

(a) Experimentally measured two-dimensional momentum distributions of correlated atomic ions ${\mathrm{O}}^{+}+{\mathrm{C}}^{+}+{\mathrm{O}}^{+}$ and (b) kinetic energy release (KER) correlation diagram for two ${\mathrm{O}}^{+}$ ions generated in the fragmentation of $\mathrm{CO}_2{}^{3+}$ in 800 nm, 24 fs linearly polarized laser fields with an intensity of $1\times {10}^{15}\mathrm{W}/{\mathrm{cm}}^2$. The data outside the circle come from nonsequential fragmentation and inside the circle from sequential fragmentation.

Figure 2

Newton plot for three-body fragmentation of $\mathrm{CO}_2{}^{3+}$ in intense laser fields. (a) Nonsequential fragmentation and (b) sequential fragmentation. The circle marked by the red dashed line is clear proof of the existence of a rotating intermediate ${\mathrm{CO}}^{2+}$ in the sequential fragmentation.

Figure 3

(a) Asymptotic angle ${\mathrm{O}}^{+}\mathrm{\text{:}}{\mathrm{O}}^{+}$ between the momentum vectors of the two ${\mathrm{O}}^{+}$ (b) ${\mathrm{C}}^{+}$ KER and (c) total KER generated from fragmentation of $\mathrm{CO}_2{}^{3+}$ in intense laser fields. Nonsequential fragmentation (red dashed line) and sequential fragmentation (black solid line).

Figure 4

Coulomb potential and ab initio potential of $\mathrm{CO}_2{}^{3+}$.