Kobayashi, YukiChang, Kristina F.Zeng, TaoNeumark, Daniel M.Leone, Stephen R.2020-04-172020-04-172019-07-05Science (July 5, 2019): 79-83.https://doi.org/10.1126/science.aax0076https://hdl.handle.net/10315/37193The 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.enArticlehttps://science.sciencemag.org/https://www.aaas.org/https://science.sciencemag.org/content/365/6448/79