Non vertical ionization-dissociation model for strong IR induced dissociation dynamics of ${{D}_{2}}O^{2+}$

Abstract

In attosecond science, a formidable challenge remains: addressing the laser coupling between electron states from different charged molecular states during strong laser-induced molecular dynamics, particularly when the nuclei move rapidly and the Born-Oppenheimer approximation (BOA) no longer applies. To overcome these difficulties, we have developed the Strong Laser Induced non-adiabatic Multi-Ionic-Multi Electric States (SLIMIMES) approach. We validate our model using a showcase example: water dissociation under strong infrared (IR) laser pulses. Our investigation reveals the predominant role of a non-vertical dissociation pathway in the photon-ionization dissociation (PID) process of $\mathrm{D_{2}O^{2+}}$. This pathway originates from neutral $\mathrm{D_{2}O}$, which undergoes vertical multi-photon-single-ionization, reaching the intermediate dissociation states of $\mathrm{D_{I} + OD_{II}^{+} (2^{3}\Sigma)}$ within $\mathrm{D_{2}O^{+}}$. Subsequently, $\mathrm{OD_{II}^{+} (2^{3}\Sigma)}$ dissociates into $\mathrm{O^{+} + D_{II}}$, with both $\mathrm{D_{I}}$ and $\mathrm{D_{II}}$ fragments potentially ionizing an electron during interaction with the IR laser. This sequential PID pathway significantly contributes to the dissociation yields of water dication. Our calculations are consistent with recent experimental data, which focus on measuring the branching ratio of water dication dissociation. We aim for our model to provide a deeper understanding and a fresh perspective on the coupling between electron and nuclear dynamics induced by a strong IR laser field.