Sequential and concerted C–C and C–O bond dissociation in the Coulomb explosion of 2-propanol
Dror M. Bittner, Krishnendu Gope, Ester Livshits, Roi Baer, Daniel Strasser
Abstract
We study the competing mechanisms involved in the Coulomb explosion of 2-propanol CH32CHOH2+ dication, formed by an ultrafast extreme ultraviolet pulse. Over 20 product channels are identified and characterized using 3D coincidence imaging of the ionic fragments. The momentum correlations in the three-body fragmentation channels provide evidence for a dominant sequential mechanism, starting with the cleavage of a C–C bond, ejecting CH3+ and CH3CHOH+ cations, followed by a secondary fragmentation of the hydroxyethyl cation that can be delayed for up to a microsecond after ionization. The C–O bond dissociation channels are less frequent, involving proton transfer and double proton transfer, forming H2O+ and H3O+ products, respectively, and exhibiting mixed sequential and concerted character. These results can be explained by the high potential barrier for the C–O bond dissociation seen in our ab initio quantum chemical calculations. We also observe coincident COH+ + C2Hn+ ions, suggesting exotic structural rearrangements, starting from the Frank–Condon geometry of the neutral 2-propanol system. Remarkably, the relative yield of the H3+ product is suppressed compared with methanol and alkene dications. Ab initio potentials and ground state molecular dynamics simulations show that a rapid and direct C–C bond cleavage dominates the Coulomb explosion process, leaving no time for H2 roaming, which is a necessary precursor to the H3+ formation.