Strong-field double ionization of formic acid leading to hydrogen elimination and multi-body fragmentation*

We examine multibody fragmentation of formic acid dications, produced by ultrashort intense laser pulses, using coincidence momentum imaging and deuterium tagging to distinguish the hydrogen sites.  Our measurements indicate that double hydrogen elimination leads to 3- and 4-body breakup, specifically H + D + CO₂²⁺ and H + D + O⁺ + CO⁺, respectively. The latter breakup channel, which undergoes sequential fragmentation, also proceeds via the same metastable dication, CO₂²⁺, but with shorter lifetimes than the CO₂²⁺ dications detected intact. This intriguing sequential breakup is identified using native frames analysis. Simulations are needed to confirm the signature of the sequential process because of the inferior momentum resolution of breakup channels for which not all fragments are detected.