Ultrafast electron diffraction: structures in dissociation dynamics of Fe(CO)_5

We report on the application of ultrafast electron diffraction (UED) to the study of complex molecular reactions, the dissociation of Fe(CO)_5. Snapshots of the diffraction images were recorded at different reaction times. The reaction was initiated by a femtosecond pulse and clocked accurately within 2 ps. The dissociation is complete in less than 10 ps and we identify major product distributions and structures; Fe(CO)_2, Fe(CO) and Fe in the branching ratio of ca. 2:5:5. The C–O distance becomes longer, relative to that of Fe(CO)_5, suggesting a non-systematic weaker C–O bond in Fe(CO)_2 and Fe(CO) fragments. The temporal diffraction-difference method greatly enhances the ability of recording structural changes in UED.