Ultrafast Proton Transfer Dynamics on the Repulsive Potential of the Ethanol Dication: Roaming-Mediated Isomerization versus Coulomb Explosion

Abstract

If a molecular dication is produced on a repulsive potential energy surface (PES), it normally dissociates. Before that, however, ultrafast nuclear dynamics can change the PES and significantly influence the fragmentation pathway. Here, we investigate the electronimpact-induced double ionization and subsequent fragmentation processes of the ethanol molecule using multiparticle coincident momentum spectroscopy and ab initio dynamical simulations. For the electronic ground state of the ethanol dication, we observe several fragmentation channels that cannot be reached by direct Coulomb explosion (CE) but require preceding isomerization. Our simulations show that ultrafast hydrogen or proton transfer (PT) can stabilize the repulsive PES of the dication before the direct CE and form intermediate H 2 or H 2 O. These neutrals stay in the vicinity of the precursor, and roaming mechanisms lead to isomerization and finally PT resulting in emission of H 3 + or H 3 O + . The present findings can help to understand the complex fragmentation dynamics of molecular cations.

Formation of H3+ from ethane dication induced by electron impact

“…To gain more insight into the H 3 + formation dynamics, we carry out quantum chemistry calculations for the dissociation of ground-state C 2 H 6 2+ . The theoretical analysis shows that the H 3 + emission channel starts from a stabilization process that is similar to the case of ethanol 4 . channel CH 3 + -CH 3 + from the rigid and relaxed scan (C 1 symmetry for each of the scan step) are shown in Fig.…”

“…The noticeable matching between the experimental and theoretical results indicates that the ground-state dissociation plays a prominent role in the fragmentation of C 2 H 6 2+ dications. The crucial role of the ground-state dissociation has been also revealed in the fragmentation of other molecular dications 4,14 . Therefore, it is reasonable in the following we consider the molecular dissociation only on the ground-state PES of ethane dications.…”

Roadmap on dynamics of molecules and clusters in the gas phase

“…Recently, Erdmann et al [115] efficiently combined the PES, MD and MC for description of the irradiation driven chemistry. Chemical transformations induced by another sources such as (i) X-ray in the mixed waterammonia clusters focusing on the microscopic observable [116] and (ii) electron impact showing H-migration in ethanol [117] were efficiently combined with PES and MD methodology. Interesting reactivity driven by lowenergy atomic and molecular ions formed by galactic cosmic rays in the Earth's atmosphere of highly oxygenated molecule has been studied focusing on both microscopic and molecular level understanding of nucleation, binding, evaporation, thermal effects, etc.…”

Controlling H3+ Formation From Ethane Using Shaped Ultrafast Laser Pulses

“…The intramolecular migration of hydrogen continues to be an active area of investigation in ultrafast science [1][2][3][4][5][6][7][8][9][10][11] with implications for topics ranging from combustion [12] to peptide dissociation [13] and characterizing conformational differences in molecules [14,15]. In some cases the migration of hydrogen leads to the formation of new molecular ions, such as H + 3 [5,[16][17][18][19][20][21], by processes such as H 2 roaming or double hydrogen migration [18,19,22,23].…”