Metastable excitation of sputtered silver atoms

Neutral atoms sputtered from a polycrystalline silver surface under bombardment with 15 keV Ar⁺ ions were investigated by resonant multiphoton ionization in combination with time-of-flight mass spectrometry. Electronically excited Ag atoms ejected in the metastable 4d⁹5s^{2 2}D_5/2 state (excitation energy 3.75 eV) were ionized by a frequency doubled tunable dye laser using a resonant single photon transition into the autoionizing 4d⁹5s(³D)5p ²D_5/2 state. Ground state silver atoms were detected by means of a resonant two photon ionization scheme involving the intermediate 4d¹⁰(¹S)5p ²P⁰ state. Both two and one color schemes were employed, the latter working via resonant excitation of Rydberg states and subsequent field ionization. The total population as well as the velocity distribution of sputtered metastable and ground state atoms were determined from the saturation behavior of the photoionization process and the flight time of the ejected neutral species between the ion bombarded surface and the ionization volume