Geometric Dependence of Strong Field Enhanced Ionization in D$_{2}$O

TL;DR

This study investigates how the orientation of a D₂O molecule relative to a strong laser field influences its ionization pathways, revealing that molecular geometry significantly affects ionization enhancement and dissociation outcomes.

Contribution

It provides new insights into the geometric dependence of strong-field enhanced ionization in D₂O, highlighting the role of molecular orientation in ionization dynamics.

Findings

Dication dissociation dominates when polarization is out of the molecular plane.

Trication dissociation is dominant when polarization aligns with the D-D axis.

Enhanced ionization drives triply charged breakup, suppressed along the C₂v axis.

Abstract

We have studied strong-field enhanced dissociative ionization of D$_{2}$O in 40 fs, 800 nm laser pulses with focused intensities of $< 1 - 3 \times 10^{15}W/cm^2$ by resolving the charged fragment momenta with respect to the laser polarization. We observe dication dissociation into OD$^{+}$/D$^{+}$ dominates when the polarization is out of the plane of the molecule, whereas trication dissociation into O$^{+}$/D$^{+}$/D$^{+}$ is strongly dominant when the polarization is aligned along the D-D axis. Dication dissociation into O/D$^{+}$/D$^{+}$, and O$^{+}$/D$_2$$^{+}$ is not seen, nor is there any significant fragmentation into multiple ions when the laser is polarized along the C$_{2v}$ symmetry axis of the molecule. Even below the saturation intensity for OD$^{+}$/D$^{+}$, the O$^{+}$/D$^{+}$/D$^{+}$ channel has higher yield. By analyzing how the laser field is oriented within the molecular frame for both channels, we show that enhanced ionization is driving the triply charged three body breakup, but is not active for the doubly charged two body breakup. We conclude that laser-induced distortion of the molecular potential suppresses multiple ionization along the C$_{2v}$ axis, but enhances ionization along the D-D direction.