Direct imaging of curve-crossing dynamics in IBr by attosecond transient absorption spectroscopy
Chang, Kristina F.
Neumark, Daniel M.
Leone, Stephen R.
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The electronic character of photoexcited molecules can abruptly change at avoided crossings and conical intersections. Here, we report direct spectroscopic imaging of such nonadiabatic processes in a prototype molecule, iodine monobromide (IBr), using extreme-ultraviolet (XUV) attosecond transient absorption spectroscopy. A few-femtosecond visible pulse resonantly excites the B(3Π0+ ) state and the accompanying dissociation dynamics are tracked by an attosecond XUV pulse that simultaneously probes the I-4d and Br-3d core-level ab- sorption edges. Direct comparison with quantum mechanical simulations unambiguously identifies the core-level absorption features associated with adiabatic and diabatic channels at the avoided crossing that is accessed by one-photon and two-photon visible-excitation processes. The results delineate rapid switching of valence-orbital vacancies from σ∗ to π/π∗ ensuing at the avoided crossing.