We report the fragmentation dynamics of double ionization of tetrahydrofuran (THF) induced by electron impact ( E 0 = 200 eV). Using a multiparticle coincidence momentum spectrometer, the hydrogen molecule (H 2 ) production channel, i.e., double ionization and fragmentation of THF ++ -> H 2 + C 3 H 5 + + CHO + , is observed and identified using an ion -ion coincidence map and the correlated projectile energy -loss spectrum. The measured kinetic energy release, combined with ab initio molecular -dynamics simulations and high-level potential energy surface (PES) calculations, reveals the detailed fragmentation dynamics of the H 2 production channel. From the measured energy -loss spectrum, we determine the initial ionization mechanism of the fragmentation channel as a double -ionization excited state (3.3 eV above the ground state). The PES calculations reveal several H 2 formation pathways, which are all below the energy of the excited state and hence can proceed barrierless. We find that the H 2 formation and ejection occur on an ultrafast timescale (approximately 50 fs), which is followed by ring opening via the C-O bond cleavage and ultimate Coulomb explosion. The present observation of the state -resolved fragmentation mechanism and dynamics is expected to provide valuable insights into the formation process of hydrogen molecules in the interstellar medium, as well as hydrogen storage and production.
