Dissociative multiple ionization of carbon dioxide dimers in intense femtosecond laser fields

Abstract

Molecular dimers have attracted much attention in the study of molecular structure and dynamics due to their complex interactions involving both weak van der Waals and strong covalent bonds. We investigate the dissociative ionization of carbon dioxide dimers exposed to intense femtosecond laser fields. The angular distributions of ionic fragments of the breakup channels ${({\mathrm{CO}}_{2})}_{2}{}^{2+}\ensuremath{\rightarrow}{\mathrm{CO}}_{2}^{+}+{\mathrm{CO}}_{2}^{+}$ and ${({\mathrm{CO}}_{2})}_{2}{}^{3+}\ensuremath{\rightarrow}{\mathrm{CO}}_{2}{}^{2+}+{\mathrm{CO}}_{2}^{+}$ strongly depend on the laser intensity. Simulations based on time-dependent density-functional theory reproduce the experimental observations qualitatively and show that the angular distribution of fragments is determined by the angle-dependent orbital ionization probability and the relative contributions of different orbitals, both of which are intensity sensitive. By comparing the ionization of the dimer with ${\mathrm{CO}}_{2}$ monomer, we find that the weak van der Waals bond and molecular geometry in the dimer play considerable roles. This work extends significantly earlier studies of simple linear covalent bond molecules.