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Mapping Wave Packet Bifurcation at a Conical Intersection in CH3I by Attosecond XUV Transient Absorption Spectroscopy
preprintsubmitted on 08.05.2021, 17:33 and posted on 11.05.2021, 06:25 by Kristina Chang, Han Wang, Sonia Marggi Poullain, David Prendergast, Daniel Neumark, Stephen Leone
Extreme ultraviolet (XUV) transient absorption spectroscopy has emerged as a sensitive tool for mapping the real-time structural and electronic evolution of molecules. Here, attosecond XUV transient absorption is used to track dynamics in the A-band of methyl iodide (CH3I). Gaseous CH3I molecules are excited to the A-band by a UV pump (277 nm, ∼20 fs) and probed by attosecond XUV pulses targeting iodine I(4d) core-to-valence transitions. Owing to the excellent temporal resolution of the technique, passage through a conical intersection is mapped through spectral signatures of nonadiabatic wave packet bifurcation observed 15 ± 4 fs following UV photoexcitation. The observed XUV signatures and time dynamics are in agreement with previous simulations [H. Wang, et al. J. Chem. Phys. 151, 124106 (2019)]. Due to the short duration of the UV pump pulse, coherent vibrational motion in the CH3I ground state along the C-I stretch mode (538 ± 7 cm-1) launched by resonant impulsive stimulated Raman scattering and dynamics in multiphoton excited states of CH3I are also detected.