Low-lying Negative Ion States Probed in Potassium - Ethanol Collisions

Abstract

Dissociative electron transfer in collisions between neutral potassium atoms and neutral ethanol molecules yields mainly OH^-, followed by C₂H₅O^-, O^-, CH₃ ^- and CH₂ ^-. The dynamics of negative ions have been investigated by recording time-of-flight mass spectra in a wide range of collision energies from 17.5 to 350 eV in the lab frame, where the branching ratios show a relevant energy dependence for low/intermediate collision energies. The dominant fragmentation channel in the whole energy range investigated has been assigned to the hydroxyl anion in contrast to oxygen anion from dissociative electron attachment (DEA) experiments. This result shows the relevant role of the electron donor in the vicinity of the temporary negative ion formed allowing access to reactions which are not thermodynamically attained in DEA experiments. The electronic state spectroscopy of such negative ions, was obtained from potassium cation energy loss spectra in the forward scattering direction at 205 eV impact energy, showing a prevalent Feshbach resonance at 9.36±0.10 eV with ${\sigma }_{OH}^{{}^{*}}/{\sigma }_{CH}^{{}^{*}}$ character, while a less pronounced ${\sigma }_{OH}^{{}^{*}}$ contribution assigned to a shape resonance has been obtained at 3.16±0.10 eV. Quantum chemical calculations for the lowest-lying unoccupied molecular orbitals in the presence of a potassium atom have been performed to support the experimental findings.

Keywords: Charge transfer; Mass spectrometry.