Three-body fragmentation of formic acid dications and trications produced by strong-field ionization

Formic acid is amenable to the study of three- and four-body molecular dynamics because it is a relatively complex molecule despite having only five atoms. Here we highlight coincidence momentum imaging measurements of two fragmentation channels of HCOOD following multiple ionization by 780 nm, 25 fs, 2×10¹⁵ W/cm² laser pulses. Triple ionization leading to D⁺ + O⁺ + HCO⁺ occurs via concerted breakup as well as two sequential processes, proceeding via either O⁺ + HDCO²⁺ or D⁺ + HCO₂²⁺ intermediates. The two sequential processes are identified and separated using the native frames analysis method. Double ionization leading to H + D + CO⁺ + O⁺ proceeds through the metastable CO₂²⁺ intermediate following double hydrogen elimination, leading to fragmentation to CO⁺ + O⁺ over a range of timescales.