Formation of H3O+ in the Ionization and Fragmentation of Ethanol Induced by Electron Beam Irradiation

Abstract

The single ionization and dissociation of ethanol molecules induced by low-energy electrons ( $E_0=90\text{eV}$ ) are investigated using multiparticle coincident momentum spectroscopy. By detecting two outgoing electrons ( $e_1$ and $e_2$ ) and one fragment ion in coincidence, we obtain the energy deposition ( $E_0-E_1-E_2$ ) during electron ionization of the molecule, i.e., the binding energy spectra, for production of the different ionic fragments C2H5OH+, C2H4OH+, COH+, and H3O+. These data allow us to study the ionization channels for different ionic products. In particular, we focus on H3O+ as a product of double hydrogen migration. It is found that this channel mainly originates from the ionization of outer-valance orbitals (3a ${}^{″}$ ,10a ${}^{\prime }$ , 2a ${}^{″}$ , 9a ${}^{\prime }$ , 8a ${}^{\prime }$ , 1a ${}^{″}$ , and 7a ${}^{\prime }$ ). Additionally, there are minor contributions from the inner-valence orbitals such as 6a ${}^{\prime }$ , 5a ${}^{\prime }$ , and 4a ${}^{\prime }$ . Quantum chemistry calculations show two fragmentation pathways: concerted and sequential processes for formation of H3O+.