Investigating transient molecular structure is one of the fundamental tasks in physics, chemistry and biology. Femtosecond laser coulomb explosion imaging has been exhibited to be a feasible approach to monitoring transient molecular structure, in which the molecule is rapidly ionized by intense femtosecond laser field and the multiply charged molecular ion is quickly fragmented. The molecular structure is then deduced from momentum vectors of correlated fragments. However, this method still remains challenging for polyatomic molecules because of their complicated fragmentation dynamics. The main question lies in whether the chemical bonds break through a sequential or a non-sequential process.

Very recently, Prof. Chengyin Wu, Prof. Qihuang Gong et al systematically studied three-body fragmentation dynamics of carbon dioxide tri-cation in intense femtosecond laser fields. Three-dimensional momenta were precisely acquired for the three correlated atomic ions through three-body coincidence measurement. Non-sequential and sequential fragmentation of carbon dioxide tri-cation were precisely separated and unambiguously identified by developing kinetic energy correlation diagram and Newton plot. With the high-level ab initio potential of carbon dioxide tri-cation and accurate three-dimensional momentum vectors of the atomic ions, the geometric structure of carbon dioxide tri-cation before fragmentation was reconstructed, which turns out to be close to that of the neutral carbon dioxide molecule before laser irradiation. The study indicated that Coulomb explosion is a promising approach to imaging geometric structures of polyatomic molecules if the fragmentation dynamics can be clearly clarified and the accurate dissociation potential is provided for multiply charged molecular ions. The work has been published by the Phys. Rev. Lett. (C. Wu et al “Nonsequential and sequential fragmentation of CO23+ in intense laser fields”, Phys. Rev. Lett. 110, 103601 (2013), http://prl.aps.org/abstract/PRL/v110/i10/e103601http://prl.aps.org/abstract/PRL/v109/i4/e043001).