Depletion of the excited state population in negative ions using laser photodetachment in a gas-filled RF quadrupole ion guide

Abstract

The depopulation of excited states in beams of negatively charged carbon and silicon ions was demonstrated using collisional detachment and laser photodetachment in a radio-frequency quadrupole ion guide filled with helium. The high-lying, loosely bound 2D excited state in C− was completely depleted through collisional detachment alone, which was quantitatively determined within 6%. For Si− the combined signal from the population in the 2P and 2D excited states was only partly depleted through collisions in the cooler. The loosely bound 2P state was likely to be completely depopulated, and the more tightly bound 2D state was partly depopulated through collisions. 98(2)% of the remaining 2D population was removed by photodetachment in the cooler using less than 2 W laser power. The total reduction of the excited population in Si−, including collisional detachment and photodetachment, was estimated to be 99(1)%. Employing this novel technique to produce a pure ground state negative ion beam offers possibilities of enhancing selectivity, as well as accuracy, in high-precision experiments on atomic as well as molecular negative ions.