Femtosecond dynamics of Fe(CO)(5) photodissociation at 267 nm studied by transient ionization

We found bye consecutive processes with time constants 21, 15, 30, 47, and 3300 fs in Fe(CO)(5) after excitation at 267 nm in the gas phase. The first four represent a continuous pathway of the molecule from the Franck-Condon region down to the lowest singlet state (S-0) of Fe(CO)(4) through a chain of Jahn-Teller-induced conical intersections. The motion before dissociati on initially involves more than one of the equatorial ligands, but then eli minates only one CO. The product Fe(CO)(4) is initially generated in its fi rst excited singlet state S-1, then it relaxes to S-0 in 47 fs via a triply degenerate conical intersection at tetrahedral geometry. The pathway for t his process involves pseudorotation of the ligands. The fifth step is assig ned to thermal elimination of a second CO. Intersystem crossing to the trip let ground states of Fe(CO)(4) and Fe(CO)(3) takes more than 500 ps.