SF6 Negative Ion Formation in Charge Transfer Experiments

In the present work, we report an update and extension of the previous ion-pair formation study of Hubers, M.M.; Los, J. <i>Chem. Phys.</i><b>1975</b>, <i>10</i>, 235-259, noting new fragment anions from time-of-flight mass spectrometry. The branching ratios obtained from the negative ions formed in K + SF₆ collisions, in a wide energy range from 10.7 up to 213.1 eV in the centre-of-mass frame, show that the main anion is assigned to SF₅^- and contributing to more than 70% of the total ion yield, followed by the non-dissociated parent anion SF₆^- and F^-. Other less intense anions amounting to <20% are assigned to SF₃^- and F₂^-, while a trace contribution at 32u is tentatively assigned to S^- formation, although the rather complex intramolecular energy redistribution within the temporary negative ion is formed during the collision. An energy loss spectrum of potassium cation post-collision is recorded showing features that have been assigned with the help of theoretical calculations. Quantum chemical calculations for the lowest-lying unoccupied molecular orbitals in the presence of a potassium atom are performed to support the experimental findings. Apart from the role of the different resonances participating in the formation of different anions, the role of higher-lying electronic-excited states of Rydberg character are noted.