Abstract
Conical intersections between electronic states often dictate the chemistry of photoexcited molecules. Recently developed sources of ultrashort extreme ultraviolet (XUV) pulses tuned to element-specific transitions in molecules allow for the unambiguous detection of electronic state-switching at a conical intersection. Here, the fragmentation of photoexcited iso-propyl iodide and tert-butyl iodide molecules (i-C(3)H(7)I and t-C(4)H(9)I) through a conical intersection between (3)Q(0)/(1)Q(1) spin-orbit states is revealed by ultrafast XUV transient absorption measuring iodine 4d core-to-valence transitions. The electronic state-sensitivity of the technique allows for a complete mapping of molecular dissociation from photoexcitation to photoproducts. In both molecules, the sub-100 fs transfer of a photoexcited wave packet from the (3)Q(0) state into the (1)Q(1) state at the conical intersection is captured. The results show how differences in the electronic state-switching of the wave packet in i-C(3)H(7)I and t-C(4)H(9)I directly lead to differences in the photoproduct branching ratio of the two systems.