PHOTODETACHMENT FROM ANIONS IN A DRIFT CELL - APPLICATION TO SF6- AT 337 NM

A novel technique is introduced for the study of photodetachment from gas phase anions drifting in the electric field between two parallel e lectrodes. The anions are generated by attachment of photoelectrons to neutral molecules. The electrons are injected from the cathode by an excimer laser pulse. The transient molecular anions formed on free ele ctron attachment are rapidly converted into their ground state by coll isions with the buffer gas. Photodetachment from the drifting ground s tate anions is then effected by a second, delayed pulse from a nitroge n laser. The technique is applied to SF6- at 337 nm. Experiments conce rning photodetachment from SF6- are scarce and rather conflicting. Fro m the results available till now it is not clear whether or not photod etachment occurs for wavelengths lambda greater-than-or-equal-to 310 n m. We demonstrate here that SF6- in fact undergoes photodetachment at 337 nm with a cross-section on the 10(-18) cm2 scale. The implications for the electronic and geometrical structure of SF6- are discussed.