Ground state (athinsp;5D) and metastable excited state (athinsp;5Fandathinsp;3F) iron atoms have been produced by visible multiphoton dissociation of Fe(CO)5at 552 nm in a static pressure gas cell at room temperature. The distribution of iron atoms among these states has been measured by using a pump and probe arrangement in which the probe laser pulse excites resonance fluorescence from iron atoms at variable time delay following the photolysis pulse. Collisional relaxation processes of metastableathinsp;5Fandathinsp;3Firon atoms have been investigated by using a simple model to describe the main features of the overall relaxation process. Results for a variety of quenching gases including N2O, C2H4O, and O2indicate that relaxation occurs mainly by transitions between adjacent multiplets, with little intermediate intramultiplet relaxation and no detectable removal by chemical reaction. An interpretation of these results is given in terms of schematic potential energy curves which represent the bonding capabilities of specific electronic configurations of iron atoms. These curves are discussed in an accompanying paper on studies of chemical reactions of ground state iron atoms.
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